Fatal systemic (paradoxical) air embolism diagnosed by postmortem funduscopy

Air embolism is often unrecognized and underreported. Published case reports or case series describe only rare fundal examinations of retinal air emboli (RAE)-a distinctive sign of systemic air embolism. We report an infant, found unresponsive at home, who died in the emergency department after unsuccessful resuscitative efforts. Before the autopsy, diagnostic RAE were recognized and imaged during postmortem funduscopy. Postmortem radiography and an autopsy confirmed systemic (paradoxical) air embolism due to inflicted abdominal and thoracic blunt force injuries. While a few descriptions and illustrations of RAE occur in case reports, we found no published photographic images of RAE in infants, children, or adults. This case report describes and photographically documents classic RAE associated with fatal systemic (paradoxical) air embolism. Complementing postmortem radiography and judicious autopsy techniques, the detection of RAE can aid pathologists in diagnosing systemic air embolism.

Maternal and fetal death at 22 weeks following uterine rupture at the site of the placenta percreta in a C-section scar

Placenta percreta is the abnormal invasion of the placenta through the myometrium and serosa of the uterus. It is the most invasive of the placenta accreta spectrum followed by placenta increta. This paper presents a case of a maternal and fetal death in the second trimester due to rupture of the uterus at the site of placenta percreta in a C-section scar. Postmortem MRI showed a large hemoperitoneum and thinning of the anterolateral uterine wall. Internal examination revealed two liters of blood in the abdomen and rupture of the anterolateral uterine wall at the site of placenta percreta in a previous C-section scar. Placenta percreta is a rare complication of pregnancy, however, it is becoming more common with the increasing rate of C-section, the most common and significant risk factor.

Pharmacological induction of pancreatic islet cell transdifferentiation: relevance to type I diabetes

Type I diabetes (T1D) is an autoimmune disease in which an immune response to pancreatic β-cells results in their loss over time. Although the conventional view is that this loss is due to autoimmune destruction, we present evidence of an additional phenomenon in which autoimmunity promotes islet endocrine cell transdifferentiation. The end result is a large excess of δ-cells, resulting from α- to β- to δ-cell transdifferentiation. Intermediates in the process of transdifferentiation were present in murine and human T1D. Here, we report that the peptide caerulein was sufficient in the context of severe β-cell deficiency to induce efficient induction of α- to β- to δ-cell transdifferentiation in a manner very similar to what occurred in T1D. This was demonstrated by genetic lineage tracing and time course analysis. Islet transdifferentiation proceeded in an islet autonomous manner, indicating the existence of a sensing mechanism that controls the transdifferentiation process within each islet. The finding of evidence for islet cell transdifferentiation in rodent and human T1D and its induction by a single peptide in a model of T1D has important implications for the development of β-cell regeneration therapies for diabetes.

Gene regulation in an MCF-7 cell line that naturally expresses an estrogen receptor unable to directly bind DNA

In the described studies, we have developed a variant of the MCF-7 cell line, M-ERd3/g8, for analysis of 17-beta-estradiol (E2)-action without direct DNA interaction by E2-receptors. M-ERd3/g8 cells principally express the estrogen receptor alpha (ER) form ERDelta3 which, due to skipping of exon 3, lacks the second zinc finger of ER that is required for direct DNA interaction. This was achieved by introduction of siRNA targeting exon 3 to a Tamoxifen-selected MCF-7 variant, TMX 2-11, expressing approximately equal amount of full-length ER and ERDelta3 proteins. M-ERd3/g8 cells exhibited a normal nuclear ER localization, and ERDelta3 expression levels were similar to those for full-length ER protein in MCF-7 cells. Ser 118 phosphorylation of the ERDelta3 was triggered by E2 treatment. The expression of several well characterized E2-responsive markers was strongly modified in the M-ERd3/g8 cells. The E2-induction of progesterone receptor (PR) and HEM45 mRNAs was abolished. The effect on pS2 mRNA expression was complex: the pS2 mRNA levels fell approximately 50-fold in control M-ERd3/g8 cells. There was E2-induction of pS2-expression but with an altered temporal pattern. This was blocked by inhibitors of the p42/44 mitogen activated protein (MAP) kinase and inositol triphosphate (PI3) kinase pathways suggesting a role for cytoplasmic signaling pathways. Gene array analysis and real-time polymerase chain reaction (PCR) studies identified several genes whose expressions were induced in E2-treated M-ERd3/g8 cells. These included A-Myb, a homolog to the avian myoblastosis virus oncogene, carbonic anhydrase XII (CAXII), chemokine ligand 12 (CXCL-12), early growth response 3 (EGR 3), fibrinogen B beta (FibBbeta), along with serine protease 23 (SPUVE). The responses fell into several temporal patterns. A-Myb, CAXII, CXCL-12 and EGR 3 were E2-induced within 2 h. The expression of CXCL-12 and EGR 3 was persistent to 24 h, while that of A-Myb and CAXII was not persistent in M-ERd3/g8 cells. FibBbeta and SPUVE expression was not induced until times later than 6 h. Expression of none of the genes was elevated prior to 2 h, but the utilization of a 24 h time point for the gene array analysis may have eliminated the most transiently responsive genes. Immediate early 3 (IE3) was down-regulated by E2 in the M-ERd3/g8 cells but was transiently up-regulated during the 2-6 h period in MCF-7 cells. Basal levels of several of the genes were strongly reduced in M-ERd3/g8, compared to MCF-7. The studies suggest that M-ERd3/g8 cells provide a new model for studies of E2-action without direct ER binding to DNA and where E2-action must be via alternate pathways.

A critical role for B cells in the development of memory CD4 cells

Activated B cells express high levels of class II MHC and costimulatory molecules and are nearly as effective as dendritic cells in their APC ability. Yet, their importance as APC in vivo is controversial and their role, if any, in the development of CD4 memory is unknown. We compared responses of CD4 cells from normal and B cell-deficient mice to keyhole limpet hemocyanin over 6 mo and observed diminished IL-2 production by cells primed in the absence of B cells. This was due to lower frequencies of Ag-responsive cells and not to decreased levels of IL-2 secretion per cell. The absence of B cells did not affect the survival of memory CD4 cells since frequencies remained stable. Despite normal dendritic cell function, multiple immunizations of B cell-deficient mice did not restore frequencies of memory cells. However, the transfer of B cells restored memory cell development. Ag presentation was not essential since B cells activated in vitro with irrelevant Ag also restored frequencies of memory cells. The results provide unequivocal evidence that B cells play a critical role in regulating clonal expansion of CD4 cells and, as such, are requisite for the optimal priming of memory in the CD4 population.

Regulation of development and function of memory CD4 subsets

Immunologic memory refers to the dramatic response to previously encountered antigen (Ag) that is largely controlled by CD4 T cells. Understanding how CD4 memory is regulated is essential for exploiting the immune system to protect against disease and to dampen immunopathology in allergic responses and autoimmunity. Using defined adoptive-transfer models, we are studying parameters that affect differentiation of memory CD4 cells in vivo and have found that a complex interplay of T cell receptor signaling, costimulation, and cytokines can determine the extent of memory development and the balance of Th1 and Th2 memory subsets. On challenge, memory CD4 cells localize in sites of Ag exposure and develop into effectors that regulate memory responses. We are investigating the roles of adhesion molecules, cytokines, and chemokines in the selective recruitment of CD4 memory subsets to address mechanisms by which memory T cells provide long-lasting immunity and, in our recent studies, to determine how memory CD4 cells contribute to the development of autoimmune diabetes.

Memory CD4 cells do not migrate into peripheral lymphnodes in the absence of antigen

Memory T cells are thought to protect against previously encountered pathogens in part by preferentially recirculating through the lymphoid tissues where they were primed and where challenge with antigen (Ag) is likely to occur. In this study, we examined the distribution of memory CD4 cells after priming, and analyzed their capacity to localize in lymph nodes after transfer to normal and Ag-primed recipients. Immunization induced a high frequency of Ag-specific CD4 cells in the primary response in draining lymph nodes and spleen. Thereafter, the numbers in lymph nodes declined dramatically whereas frequencies in the spleen were unchanged, suggesting that memory CD4 cells primarily reside in or recirculate through the spleen. Indeed, memory CD4 cells, unlike naive CD4 cells, failed to home to lymph nodes after adoptive transfer to normal recipients and were detected predominantly in the spleen for extended periods, suggesting that recirculation through lymph nodes was limited. Memory cells also did not home to lymph nodes recipients in response to specific Ag, but subsequently, recruitment that could be blocked with monoclonal antibodies to CD44 and LFA-1 and was independent of naive cells did occur. The data indicate that memory and naive CD4 cells can be distinguished on the basis of their patterns of circulation.

Islet-specific Th1, but not Th2, cells secrete multiple chemokines and promote rapid induction of autoimmune diabetes

Migration of CD4 cells into the pancreas represents a hallmark event in the development of insulin-dependent diabetes mellitus. Th1, but not Th2, cells are associated with pathogenesis leading to destruction of islet beta-cells and disease onset. Lymphocyte extravasation from blood into tissue is regulated by multiple adhesion receptor/counter-receptor pairs and chemokines. To identify events that regulate entry of CD4 cells into the pancreas, we transferred Th1 or Th2 cells induced in vitro from islet-specific TCR transgenic CD4 cells into immunodeficient (NOD.scid) recipients. Although both subsets infiltrated the pancreas and elicited multiple adhesion receptors (peripheral lymph node addressin, mucosal addressin cell adhesion molecule-1, LFA-1, ICAM-1, and VCAM-1) on vascular endothelium, entry/accumulation of Th1 cells was more rapid than that of Th2 cells, and only Th1 cells induced diabetes. In vitro, Th1 cells were also distinguished from Th2 cells by the capacity to synthesize several chemokines that included lymphotactin, monocyte chemoattractant protein-1 (MCP-1), and macrophage inflammatory protein-1alpha, whereas both subsets produced macrophage inflammatory protein-1beta. Some of these chemokines as well as RANTES, MCP-3, MCP-5, and cytokine-response gene-2 (CRG-2)/IFN-inducible protein-10 (IP-10) were associated with Th1, but not Th2, pancreatic infiltrates. The data demonstrate polarization of chemokine expression by Th1 vs Th2 cells, which, within the microenvironment of the pancreas, accounts for distinctive inflammatory infiltrates that determine whether insulin-producing beta-cells are protected or destroyed.

The recirculation of naive and memory lymphocytes

It has been clearly shown that continuous recirculation of lymphocytes is crucial for the development of primary immune responses and that naive CD4 cells are distinguished from memory CD4 cells by differences in expression of several adhesion molecules. These findings suggest that changes in migratory behavior accompany the naive to memory cell transition. This area is first reviewed and then to evaluate this hypothesis, we compare the tissue distributions of highly purified naive and memory CD4 cells after transfer to syngeneic recipients. Naive cells which express high levels of L-selectin, and low levels of alpha 4 and beta 2 integrins, and CD44 localized in secondary lymphoid organs and were detectable in these tissues and in the blood for several weeks after transfer. Memory cells, which have a reciprocal phenotype, showed a markedly different distribution, particularly with respect to tissues where entry is controlled through high endothelial venules.

Blockade of both L-selectin and alpha4 integrins abrogates naive CD4 cell trafficking and responses in gut-associated lymphoid organs

The recirculation of naive lymphocytes from blood to lymph that is initiated in high endothelial venules (HEV) of secondary lymphoid organs such as lymph nodes and Peyer's patches (PP) is regulated by multiple interactions of adhesion receptor/counter-receptor pairs involving both selectins and integrins. We showed previously that blocking of only L-selectin is sufficient to ablate trafficking of naive CD4 cells and the development of their responses in peripheral lymph nodes but not in PP where alpha4beta7 integrins are thought to primarily regulate entry. However, although antibody to alpha4 integrins partially inhibited homing of naive CD4 cells to PP and not to lymph nodes, there was no effect on the development primary responses in these tissues or spleens. Since previous studies indicate that both alpha4beta7 integrins and L-selectin regulate adhesion of naive cells to PP HEV, we examined the effect a blockade of both adhesion pathways on the recirculation of naive CD4 cells. There was no detectable homing of naive CD4 cells to PP or lymph nodes when interactions with both receptors were inhibited, resulting in a profound depletion of naive CD4 cells and loss of antigen responses in these sites. In contrast, increased numbers of naive CD4 cells and responses of higher magnitude were found in the spleen. The results demonstrate recirculation of naive CD4 cells through tissues where entry is controlled through HEV is essential for the local generation of primary responses.

Diabetes induced by Coxsackie virus: initiation by bystander damage and not molecular mimicry

Viral induction of autoimmunity is thought to occur by either bystander T-cell activation or molecular mimicry. Coxsackie B4 virus is strongly associated with the development of insulin-dependent diabetes mellitus in humans and shares sequence similarity with the islet autoantigen glutamic acid decarboxylase. We infected different strains of mice with Coxsackie B4 virus to discriminate between the two possible induction mechanisms, and found that mice with susceptible MHC alleles had no viral acceleration of diabetes, but mice with a T cell receptor transgene specific for a different islet autoantigen rapidly developed diabetes. These results show that diabetes induced by Coxsackie virus infection is a direct result of local infection leading to inflammation, tissue damage, and the release of sequestered islet antigen resulting in the re-stimulation of resting autoreactive T cells, further indicating that the islet antigen sensitization is an indirect consequence of the viral infection.

T cell memory

Immunological memory can be defined as the faster and stronger response of an animal that follows reexposure to the same antigen. By this definition, it is an operational property of the whole animal or the immune system. Memory cells express a different pattern of cell surface markers, and they respond in several ways that are functionally different from those of naive cells. Murine memory cells are CD44 high and low in the expression of activation markers such as CD25 (IL-2R), whereas human memory cells are CD45RA-, CD45RO+. In contrast to naive cells, memory cells secrete a full range of T cell cytokines and can be polarized to secrete particular restricted patterns of secretion for both CD4 and CD8 T cells. The requirements for the activation of memory cells for proliferation and cytokine production are not quite as strict as those of naive cells, but costimulation in the broad sense is required for optimum responses and for responses to suboptimum antigen concentrations. It would appear that memory cells can persist in the absence of antigenic stimulation and persist as nondividing cells. Reencounter with the same antigen can expand the population to a new, stable, higher level and generate a separate population of CD44 high effectors that may be required for protection, while competition from other antigens can drive it down to a lower stable level. It is unclear how or where memory cells arise, but once generated they have different pathways of recirculation and homing.

Echocardiographic evidence for a ductal tissue sling causing discrete coarctation of the aorta in the neonate: case report

A neonate presented to our institution with the physical findings of coarctation of the aorta. After starting prostaglandin E1 the signs and symptoms resolved despite persistent closure of the ductus arteriosus. We present echocardiographic evidence to support the contention that a ductal tissue sling contributes to the formation of juxtaductal coarctation of the aorta.

Mechanism underlying counterregulation of autoimmune diabetes by IL-4

Diabetes in nonobese diabetic (NOD) mice is an autoimmune disease characterized by the destruction of the beta cells in the pancreas. We have previously reported that transgenic expression of interleukin-4 (IL-4) counterregulates the disease process, completely protecting NOD mice from insulitis and diabetes. Here we demonstrate the presence of autoreactivity but lack of pathogenicity of the IL-4-regulated lymphocytes. The importance of T cell diversity for the protective effect of IL-4 is demonstrated through breeding with transgenic BDC2.5 mice, which have an almost exclusively monoclonal T cell repertoire. Limitation of T cell diversity abrogated the protection by IL-4. We suggest that "immune deviation" in NOD-IL-4 mice is mediated by the pancreatic tissue itself, which causes activation of distinct, nonpathogenic T cell specificities.

Interferon gamma (IFN-gamma) is necessary for the genesis of acetylcholine receptor-induced clinical experimental autoimmune myasthenia gravis in mice

Experimental autoimmune myasthenia gravis (EAMG) is an animal model of human myasthenia gravis (MG). In mice, EAMG is induced by immunization with Torpedo californica acetylcholine receptor (AChR) in complete Freund's adjuvant (CFA). However, the role of cytokines in the pathogenesis of EAMG is not clear. Because EAMG is an antibody-mediated disease, it is of the prevailing notion that Th2 but not Th1 cytokines play a role in the pathogenesis of this disease. To test the hypothesis that the Th1 cytokine, interferon (IFN)-gamma, plays a role in the development of EAMG, we immunized IFN-gamma knockout (IFN-gko) (-/-) mice and wild-type (WT) (+/+) mice of H-2(b) haplotype with AChR in CFA. We observed that AChR-primed lymph node cells from IFN-gko mice proliferated normally to AChR and to its dominant pathogenic alpha146-162 sequence when compared with these cells from the WT mice. However, the IFN-gko mice had no signs of muscle weakness and remained resistant to clinical EAMG at a time when the WT mice exhibited severe muscle weakness and some died. The resistance of IFN-gko mice was associated with greatly reduced levels of circulating anti-AChR antibody levels compared with those in the WT mice. Comparatively, immune sera from IFN-gko mice showed a dramatic reduction in mouse AChR-specific IgG1 and IgG2a antibodies. However, keyhole limpet hemocyanin (KLH)-priming of IFN-gko mice readily elicited both T cell and antibody responses, suggesting that IFN-gamma regulates the humoral immune response distinctly to self (AChR) versus foreign (KLH) antigens. We conclude that IFN-gamma is required for the generation of a pathogenic anti-AChR humoral immune response and for conferring susceptibility of mice to clinical EAMG.

L-selectin is not essential for naive CD4 cell trafficking or development of primary responses in Peyer's patches

We showed previously that L-selectin-dependent recirculation of naive CD4 cells is essential for development of primary responses in peripheral lymph nodes. Recent studies suggest that L-selectin is also required for lymphocyte entry into gut mucosal lymphoid tissues that include Peyer's patches and mesenteric lymph nodes. Here we show that anti-L-selectin antibody, MEL-14, inhibited homing of a rigorously purified, homogenous population of naive CD4 cells into both of these tissues as well as peripheral lymph nodes, directly demonstrating a role for this receptor in regulating entry into gut-associated sites. However, in intact animals, treatment with MEL-14 resulted in the loss of naive CD4 cells (CD45RBhi, CD44lo from peripheral lymph nodes but not Peyer's patches, whereas mesenteric lymph nodes were intermediate in this regard. In mice primed by parenteral immunization with keyhole limpet hemocyanin (KLH), primary CD4 responses were readily detected in both. Peyer's patches and mesenteric lymph nodes, and were not affected by exposure to MEL-14. Indeed, similar frequencies of KLH-specific CD4 cells were recovered from both of these tissues irrespective of MEL-14 treatment. The results indicate that interactions with L-selectin can be circumvented to allow entry of naive CD4 cells into Peyer's patches but not peripheral lymph nodes.

Problems with rigid seed strand lodging during prostate implantation: a proposed mechanism and solution

Since the introduction of rigid strands of radioactive seeds embedded in absorbable suture material, many brachytherapists have experienced problems with the strands lodging inside the implant needle during the deposition process. By using a scanning electron microscope, we examined some potential factors which could lead to this problem. It seems plausible that the lodging is due to two factors: prostate tissue hindering the motion of the strand initially, and friction between the strand braids and the inner surface of the needle. Both result in an "accordion effect" as the stylet applies pressure on the strand. Based on this assumption, a solution was found. A combination of using needles with a polished inner surface, and repeated clockwise and counterclockwise 360 degrees twisting of the needle about the stylet during the deposition process allows for smooth deposition of the strand at the intended location. By using this technique, one is able to exploit the potential dosimetric advantages of rigid seed strand implants without additional problems.

A direct role for IFN-gamma in regulation of Th1 cell development

IL-12 has been identified as a major cytokine influencing the differentiation of CD4 cells to a Th1 phenotype, whereas a role for IFN-gamma is controversial. We investigated the interrelationship between IL-12 and IFN-gamma in promoting Th1 responses using naive CD4 cells reactive with pigeon cytochrome c from TCR transgenics and memory CD4 cells derived by in vivo priming with KLH. Without exogenous rIL-12 or rIFN-gamma, primary and memory effectors induced by Ag or anti-CD3 and anti-CD28 secreted variable levels of IL-2 and IFN-gamma. The level of IFN-gamma secreted by effectors correlated with endogenous IFN-gamma produced in primary cultures, and anti-IFN-gamma largely inhibited the development of effectors producing IFN-gamma. With optimal TCR stimulation and costimulation, endogenous IFN-gamma, without IL-12, was sufficient to elicit Th1 cells via an autocrine mechanism, whereas with suboptimal stimulation, exogenous rIFN-gamma or rIL-12 was required for Th1 development. However, rIL-12 was more effective than rIFN-gamma, partially because rIL-12 greatly enhanced autocrine production of IFN-gamma, and optimal development of the Th1 phenotype was mediated by the synergistic actions of both cytokines. Thus, both IFN-gamma and IL-12 can independently regulate Th1 development, but because of IFN-gamma-mediated feedback, their relative contributions are determined by the conditions of T cell stimulation. The extent of differentiation to a Th1 phenotype may, therefore, depend on the availability of both APC-derived IL-12 and autocrine IFN-gamma consequent to the overall strength of T cell stimulation.

A direct role for IFN-gamma in regulation of Th1 cell development

IL-12 has been identified as a major cytokine influencing the differentiation of CD4 cells to a Th1 phenotype, whereas a role for IFN-gamma is controversial. We investigated the interrelationship between IL-12 and IFN-gamma in promoting Th1 responses using naive CD4 cells reactive with pigeon cytochrome c from TCR transgenics and memory CD4 cells derived by in vivo priming with KLH. Without exogenous rIL-12 or rIFN-gamma, primary and memory effectors induced by Ag or anti-CD3 and anti-CD28 secreted variable levels of IL-2 and IFN-gamma. The level of IFN-gamma secreted by effectors correlated with endogenous IFN-gamma produced in primary cultures, and anti-IFN-gamma largely inhibited the development of effectors producing IFN-gamma. With optimal TCR stimulation and costimulation, endogenous IFN-gamma, without IL-12, was sufficient to elicit Th1 cells via an autocrine mechanism, whereas with suboptimal stimulation, exogenous rIFN-gamma or rIL-12 was required for Th1 development. However, rIL-12 was more effective than rIFN-gamma, partially because rIL-12 greatly enhanced autocrine production of IFN-gamma, and optimal development of the Th1 phenotype was mediated by the synergistic actions of both cytokines. Thus, both IFN-gamma and IL-12 can independently regulate Th1 development, but because of IFN-gamma-mediated feedback, their relative contributions are determined by the conditions of T cell stimulation. The extent of differentiation to a Th1 phenotype may, therefore, depend on the availability of both APC-derived IL-12 and autocrine IFN-gamma consequent to the overall strength of T cell stimulation.

Lymphocyte migration into tissue: the paradigm derived from CD4 subsets

The appropriate recirculation and migration of naive, effector and memory T cells into inflamed tissue are precisely controlled by adhesive interactions with vascular endothelium. Analyses of CD4 lymphocytes have indicated that naive and antigen-experienced cells exhibit distinctive patterns of homing and recirculation, and that subsets of cells preferentially localize in different anatomical locations as a consequence of previous antigen exposure and differences in adhesion receptor usage.

Enhanced development of Th2-like primary CD4 effectors in response to sustained exposure to limited rIL-4 in vivo

Previous studies have established that cytokines regulate development of Th cell subsets from naive CD4 cells, suggesting promising therapeutic potential for cytokines that has not been fully realized, in part due to high dose toxicity. Here we examined effects of sustained delivery of low doses of rIL-4 on development of cytokine-secreting primary CD4 cells in vivo. Diffusion chambers injected with X63.Ag-653 plasmacytoma transfectants that constitutively produce rIL-4 were implanted s.c. in mice 24 to 48 h before immunization with keyhole limpet hemocyanin (KLH). Five days later at the peak of the response, KLH-specific CD4 cells from controls, which received chambers containing untransfected plasmacytoma cells, secreted primarily IL-2 and IL-4, with low levels of IFN-gamma and no IL-5 following Ag restimulation. Administration of rIL-4 enhanced IL-2 and IL-4 production by two- to fivefold, with a corresponding decrease in IFN-gamma. As frequencies of KLH-specific precursors that secreted IL-4 were unaltered, exogenous cytokine apparently affected the magnitude of IL-4 secretion by primed CD4 cells. Although IL-4 was undetectable in sera of mice carrying chambers, titers of KLH-specific IgG1 and IgG3 Ab were increased by rIL-4, whereas IgM, IgG2a, and IgG2b levels were unaltered. The results indicate that sustained delivery of low doses of cytokines at sites distant from Ag exposure can selectively potentiate development of CD4 subsets.

Enhanced development of Th2-like primary CD4 effectors in response to sustained exposure to limited rIL-4 in vivo

Previous studies have established that cytokines regulate development of Th cell subsets from naive CD4 cells, suggesting promising therapeutic potential for cytokines that has not been fully realized, in part due to high dose toxicity. Here we examined effects of sustained delivery of low doses of rIL-4 on development of cytokine-secreting primary CD4 cells in vivo. Diffusion chambers injected with X63.Ag-653 plasmacytoma transfectants that constitutively produce rIL-4 were implanted s.c. in mice 24 to 48 h before immunization with keyhole limpet hemocyanin (KLH). Five days later at the peak of the response, KLH-specific CD4 cells from controls, which received chambers containing untransfected plasmacytoma cells, secreted primarily IL-2 and IL-4, with low levels of IFN-gamma and no IL-5 following Ag restimulation. Administration of rIL-4 enhanced IL-2 and IL-4 production by two- to fivefold, with a corresponding decrease in IFN-gamma. As frequencies of KLH-specific precursors that secreted IL-4 were unaltered, exogenous cytokine apparently affected the magnitude of IL-4 secretion by primed CD4 cells. Although IL-4 was undetectable in sera of mice carrying chambers, titers of KLH-specific IgG1 and IgG3 Ab were increased by rIL-4, whereas IgM, IgG2a, and IgG2b levels were unaltered. The results indicate that sustained delivery of low doses of cytokines at sites distant from Ag exposure can selectively potentiate development of CD4 subsets.

The cytokines IL-4, IFN-gamma, and IL-12 regulate the development of subsets of memory effector helper T cells in vitro

We analyzed the development of cytokine-producing effector T cells from resting CD4 memory cells. Previously we showed that such memory effectors are induced in vivo upon re-exposure to Ag. Here we demonstrate that effectors arise in vitro when memory CD4 cells are restimulated with Ag in the presence cytokines. Resting splenic CD4 cells from KLH-primed mice that were depleted of naive cells by adult thymectomy and were exclusively of memory phenotype initially secreted high titers of IL-2 and low levels of IL-4 and IFN-gamma in response to Ag. When memory CD4 cells were restimulated for 3 to 4 days in cultures containing rIL-2 and Ab to block endogenous IFN-gamma and IL-4 secretion, Th0-like effectors that produced greatly increased levels of IL-2, IL-4, and IFN-gamma developed. rIL-4 together with rIL-2 and anti-IFN-gamma induced Th2-like cells that secreted primarily IL-4. In contrast, Th1-like effectors that produced IL-2 and IFN-gamma developed in the presence of rIL-2 and anti-IL-4. Addition of rIFN-gamma further enhanced priming for IFN-gamma secretion. rIL-12 also induced effectors that produced high levels of IFN-gamma, but little IL-2. Thus, cytokines direct the development of effector subsets from memory CD4 cells. Our results suggest that memory and naive CD4 cells undergo parallel development following Ag stimulation, initially secreting predominantly IL-2 and differentiating in response to IL-4, IFN-gamma, and IL-12 into polarized effector subsets.

The cytokines IL-4, IFN-gamma, and IL-12 regulate the development of subsets of memory effector helper T cells in vitro

We analyzed the development of cytokine-producing effector T cells from resting CD4 memory cells. Previously we showed that such memory effectors are induced in vivo upon re-exposure to Ag. Here we demonstrate that effectors arise in vitro when memory CD4 cells are restimulated with Ag in the presence cytokines. Resting splenic CD4 cells from KLH-primed mice that were depleted of naive cells by adult thymectomy and were exclusively of memory phenotype initially secreted high titers of IL-2 and low levels of IL-4 and IFN-gamma in response to Ag. When memory CD4 cells were restimulated for 3 to 4 days in cultures containing rIL-2 and Ab to block endogenous IFN-gamma and IL-4 secretion, Th0-like effectors that produced greatly increased levels of IL-2, IL-4, and IFN-gamma developed. rIL-4 together with rIL-2 and anti-IFN-gamma induced Th2-like cells that secreted primarily IL-4. In contrast, Th1-like effectors that produced IL-2 and IFN-gamma developed in the presence of rIL-2 and anti-IL-4. Addition of rIFN-gamma further enhanced priming for IFN-gamma secretion. rIL-12 also induced effectors that produced high levels of IFN-gamma, but little IL-2. Thus, cytokines direct the development of effector subsets from memory CD4 cells. Our results suggest that memory and naive CD4 cells undergo parallel development following Ag stimulation, initially secreting predominantly IL-2 and differentiating in response to IL-4, IFN-gamma, and IL-12 into polarized effector subsets.

Subverting lymph node trafficking by treatment with the Mel-14 monoclonal antibody to L-selectin does not prevent an effective host response to Sendai virus

A single 250-micrograms dose of the Mel-14 mAb to L-selectin greatly diminished the extent of L-selectin expression on lymphocytes and decreased (60 to 90%) the massive cellular recruitment to the cervical and mediastinal lymph nodes that follows intranasal infection of naive C57BL/6 mice with Sendai virus. The numbers of CD8+ CTL precursors in the mediastinal lymph nodes were considerably reduced on day 7, when compared with virus-infected mice given a control rat IgG2a, but potent CTL effectors were present in the lungs of both groups by day 10 after infection, and the overall magnitude of CTL precursor generation was not obviously compromised. The early dominance of Sendai virus-specific IgM Ab-forming cells was prolonged in the Mel-14-treated mice, whereas plasma cells producing virus-specific IgA were abnormally prominent in the lymph nodes but not in the spleen. The kinetics of virus-specific Ab-forming cells generation and the serum Ab response for the various IgG isotypes were also delayed. Thus, though L-selectin is clearly important for the localization of naive lymphocytes to regional lymph nodes, the Mel-14-treated mouse can still deal effectively with a virus that causes productive infection only in the respiratory tract. The spleen, where L-selectin does not determine lymphocyte trafficking, is a major site for the compensatory T cell and B cell responses.

Subverting lymph node trafficking by treatment with the Mel-14 monoclonal antibody to L-selectin does not prevent an effective host response to Sendai virus

A single 250-micrograms dose of the Mel-14 mAb to L-selectin greatly diminished the extent of L-selectin expression on lymphocytes and decreased (60 to 90%) the massive cellular recruitment to the cervical and mediastinal lymph nodes that follows intranasal infection of naive C57BL/6 mice with Sendai virus. The numbers of CD8+ CTL precursors in the mediastinal lymph nodes were considerably reduced on day 7, when compared with virus-infected mice given a control rat IgG2a, but potent CTL effectors were present in the lungs of both groups by day 10 after infection, and the overall magnitude of CTL precursor generation was not obviously compromised. The early dominance of Sendai virus-specific IgM Ab-forming cells was prolonged in the Mel-14-treated mice, whereas plasma cells producing virus-specific IgA were abnormally prominent in the lymph nodes but not in the spleen. The kinetics of virus-specific Ab-forming cells generation and the serum Ab response for the various IgG isotypes were also delayed. Thus, though L-selectin is clearly important for the localization of naive lymphocytes to regional lymph nodes, the Mel-14-treated mouse can still deal effectively with a virus that causes productive infection only in the respiratory tract. The spleen, where L-selectin does not determine lymphocyte trafficking, is a major site for the compensatory T cell and B cell responses.

Entry of naive CD4 T cells into peripheral lymph nodes requires L-selectin

Binding of L-selectin expressed on lymphocytes to carbohydrate ligand(s) on lymph node high endothelial venules is thought to initiate lymphocyte extravasation from blood to lymph during recirculation and localization to sites of antigen (Ag) exposure. Previous studies have shown that treatment of lymphocytes with antibody to L-selectin (MEL-14) ablates trafficking to peripheral lymph nodes (PLN). In mice, naive but not memory CD4 cells express L-selectin. To examine the role of L-selectin in helper T cell migration, we studied the effects of in vivo administration of MEL-14 on CD4 cell responses. Systemic exposure of mice to MEL-14 depleted CD4 cells expressing a naive phenotype (CD45RBhi, CD44lo) from PLN but not from spleen. The majority of residual lymph node CD4 cells exhibited the reciprocal, memory phenotype (CD45RBlo, CD44hi). MEL-14 treatment prevented priming of naive CD4 cells for proliferation and cytokine production (IL-2 and IL-4) to keyhole limpet hemocyanin in PLN draining the site of Ag injection, but not in the spleen. The results suggest that naive cells were not depleted, but rather diverted to other sites where priming occurred. The data demonstrate that L-selectin mediates extravasation of naive CD4 cells into PLN and that its function cannot be replaced by other homing receptors.

Naive versus memory CD4 T cell response to antigen. Memory cells are less dependent on accessory cell costimulation and can respond to many antigen-presenting cell types including resting B cells

Secondary responses to Ag in vivo are characterized by more rapid kinetics and greatly enhanced magnitude compared with primary responses. For CD4+ T cells, this is in part due to a greater frequency of Ag-specific memory cells, and may also reflect differences in responsiveness of memory vs naive cells to stimulation. To compare activation requirements and the role of accessory cells, naive and memory cells were stimulated with immobilized anti-CD3 in the presence or absence of APC. With anti-CD3 alone, naive cells proliferated slightly but produced no detectable IL-2, whereas memory cells proliferated well with significant IL-2 production. Increasing numbers of T-depleted APC greatly enhanced responses of naive cells to levels equivalent to those of memory cells, whereas for memory cells only IL-2 production increased slightly. The response of naive cells was equivalent in magnitude and kinetics to that of memory cells when low density APC, enriched in dendritic cells and depleted of resting B cells, were used with anti-CD3. To directly compare naive and memory responses in an Ag-specific model, we examined CD4+ cells specific for a peptide of pigeon cytochrome c fragment isolated from TCR-alpha beta transgenic mice. Naive cells were compared with 4-day activated blasts (effectors) and memory cells generated by adoptive transfer of effectors to adult thymectomized bone marrow reconstituted mice, in which the cells return to a resting state but still respond to recall Ag. Naive cells responded to Ag on dendritic cells and activated B cells but not on resting B cells or macrophages. In contrast, both memory cells and effectors were stimulated by all APCs, including resting B cells and macrophage to a limited extent. The ability of memory cells to respond to all APC types was confirmed using Ag-specific cells generated by in vivo priming with keyhole limpet hemocyanin. These results suggest that memory cells are considerably less dependent on accessory cell costimulation than naive cells, but that naive cells can respond equivalently in both magnitude and kinetics if Ag is presented on costimulatory APCs such as dendritic cells. In addition, these studies suggest that the enhanced secondary T cell response is due to a combination of the increased frequency of Ag-specific cells and their ability to react to Ag presented on a wider range of APC types, rather than an inherent capacity of memory T cells to respond better and faster.

Naive versus memory CD4 T cell response to antigen. Memory cells are less dependent on accessory cell costimulation and can respond to many antigen-presenting cell types including resting B cells

Secondary responses to Ag in vivo are characterized by more rapid kinetics and greatly enhanced magnitude compared with primary responses. For CD4+ T cells, this is in part due to a greater frequency of Ag-specific memory cells, and may also reflect differences in responsiveness of memory vs naive cells to stimulation. To compare activation requirements and the role of accessory cells, naive and memory cells were stimulated with immobilized anti-CD3 in the presence or absence of APC. With anti-CD3 alone, naive cells proliferated slightly but produced no detectable IL-2, whereas memory cells proliferated well with significant IL-2 production. Increasing numbers of T-depleted APC greatly enhanced responses of naive cells to levels equivalent to those of memory cells, whereas for memory cells only IL-2 production increased slightly. The response of naive cells was equivalent in magnitude and kinetics to that of memory cells when low density APC, enriched in dendritic cells and depleted of resting B cells, were used with anti-CD3. To directly compare naive and memory responses in an Ag-specific model, we examined CD4+ cells specific for a peptide of pigeon cytochrome c fragment isolated from TCR-alpha beta transgenic mice. Naive cells were compared with 4-day activated blasts (effectors) and memory cells generated by adoptive transfer of effectors to adult thymectomized bone marrow reconstituted mice, in which the cells return to a resting state but still respond to recall Ag. Naive cells responded to Ag on dendritic cells and activated B cells but not on resting B cells or macrophages. In contrast, both memory cells and effectors were stimulated by all APCs, including resting B cells and macrophage to a limited extent. The ability of memory cells to respond to all APC types was confirmed using Ag-specific cells generated by in vivo priming with keyhole limpet hemocyanin. These results suggest that memory cells are considerably less dependent on accessory cell costimulation than naive cells, but that naive cells can respond equivalently in both magnitude and kinetics if Ag is presented on costimulatory APCs such as dendritic cells. In addition, these studies suggest that the enhanced secondary T cell response is due to a combination of the increased frequency of Ag-specific cells and their ability to react to Ag presented on a wider range of APC types, rather than an inherent capacity of memory T cells to respond better and faster.

Rapid detection of viruses of the tick-borne encephalitis virus complex by RT-PCR of viral RNA

Studies were performed to identify a pair of primers, specific for the tick-borne encephalitis (TBE) virus complex of the Flaviviridae, with which to develop a rapid and specific identification system based on reverse transcription and the polymerase chain reaction (RT-PCR). The specificity of a putative primer pair was examined by RT-PCR of representative viruses from other antigenic complexes of the Flaviviridae and by computer sequence homology checks. All viruses of the TBE complex tested, with a single exception, were identified by RT-PCR using the identified primer pair. Accumulated data suggest that one of the putative primers identified in these studies may have flavivirus group specificity. The advantages of such a primer in the development of identification systems for all virus complexes of the Flaviviridae is discussed.

Correlation of in vitro and in vivo growth suppression of MCF-7 human breast cancer by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The purpose of this study was to compare the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the in vitro and in vivo 17 beta-estradiol (E2)-dependent growth of MCF-7 human breast cancer cells. In culture, a major component of postconfluent growth of MCF-7 cells is E2 dependent. In vivo, MCF-7 cells fail to grow as xenografts without exogenous E2 support. Thus the effect of TCDD on postconfluent MCF-7 growth in culture was compared with its effect on MCF-7 xenograft growth in immunosuppressed mice. A concentration of 10(-9) M E2 was optimal for supporting postconfluent growth of MCF-7 cells in culture into multicellular aggregates (foci) on a monolayer background. The 50% inhibitory dose of TCDD under these conditions was 3 x 10(-10) M, while E2-dependent focus development was completely inhibited by 10(-8) M TCDD. Weekly i.p. administration of TCDD (5 micrograms/kg) to mice bearing MCF-7 tumor xenografts resulted in inhibition of the tumor growth rate for the first 2 weeks, followed by recovery to the control growth rate during the third week. These recovered tumors were found to retain estrogen-dependent growth as shown by second generation transplantation studies. The p.o. route of TCDD administration yielded a similar 2-week transient suppression of growth with a concentration of 8 micrograms TCDD/kg body weight but only a 1-week growth rate latency with a 2-microgram/kg body weight dose. A single 5-micrograms/kg dose given 1 day after implantation was virtually noninhibitory. These results indicate that TCDD suppression of estrogen-dependent MCF-7 human breast cancer cell growth in vitro was predicative of a similar growth suppression of MCF-7 solid tumor xenografts in vivo. However, additional host-related factors must be involved in vivo, since suppression of tumor growth is transient. These studies provide a basis for future in vivo investigations of TCDD endocrine toxicity by using the MCF-7 tumor as a surrogate estrogen-responsive human organ and to examine the efficacy of TCDD and related Ah receptor-mediated compounds in the management of human estrogen-dependent breast cancer.

T-cell memory: new perspectives

Immunological memory provides excellent protection against a wide variety of different pathogens. Compared to the primary encounter with antigen, the secondary response is more rapid and effective. So much so, that reexposure often goes unnoticed by the host. The specific nature of memory implies that it is especially dependent on T and B cells, the cells of the immune system which recognize antigen; it follows that the changes which occur in these cells during priming must account in large part for the memory response. Here, we will summarize what is and what is not known about memory in the CD4 T-cell population.

Memory effectors: a potent, IL-4-secreting helper T cell population that develops in vivo after restimulation with antigen

Resting CD4+ memory T cells from the spleens of mice primed more than 6 wk earlier with KLH in adjuvant produce IL-2 and IL-3, but only low levels of IL-4 and IFN-gamma, and undetectable IL-5 after specific restimulation in vitro. In contrast, when previously primed mice are boosted by i.v. injection of soluble KLH, a CD4+ T cell population develops in the spleen that can produce greatly increased levels of IL-4, and variably increased IL-2, IFN-gamma, and/or IL-3. The ability of these memory effector Th cells to be restimulated to secrete cytokines is maximal by 3 days after in vivo boosting with Ag, and declines rapidly thereafter. Memory effector Th are induced in the spleens of KLH-primed mice that have been depleted of precursor T cells by thymectomy more than 25 wk previously, suggesting that they are derived from a memory T cell population. Cell separation on the basis of CD45RB or MEL-14, surface markers that are down-regulated on memory CD4+ cells, indicates that memory effector Th are in the CD45RBlo and MEL-14- subsets of CD4+ T cells. The frequency of KLH-specific splenic CD4+ T cells with the capacity to secrete cytokines in limiting dilution cultures is very low in unprimed mice (1/3 x 10(4) to 1/9 x 10(4)), but increases as much as 50-fold after priming. IL-2, but not IL-4, can be detected in the supernatants of stimulated unprimed CD4+ T cells. Both IL-2- and IL-4-producing cells are readily detected after priming, and frequencies of IL-2-secreting cells (1/250 to 1/4000) are up to ninefold greater than those for IL-4 secreting cells. Boosting elicits variable (two to eightfold) increases in the frequencies of both IL-2- and IL-4-producing CD4+ T cells. However, high IL-4 titers associated with memory effector Th function can be obtained when significant frequency changes are not detected after boosting. The data suggest that reactivation of resting memory Th in vivo induces their differentiation into effector Th with the capacity to secrete much higher levels of IL-4. Although the capacity to produce high levels of IL-4 is associated with both primary and memory CD4+ effector populations, memory effector Th are the higher producers.(ABSTRACT TRUNCATED AT 400 WORDS)

Memory effectors: a potent, IL-4-secreting helper T cell population that develops in vivo after restimulation with antigen

Resting CD4+ memory T cells from the spleens of mice primed more than 6 wk earlier with KLH in adjuvant produce IL-2 and IL-3, but only low levels of IL-4 and IFN-gamma, and undetectable IL-5 after specific restimulation in vitro. In contrast, when previously primed mice are boosted by i.v. injection of soluble KLH, a CD4+ T cell population develops in the spleen that can produce greatly increased levels of IL-4, and variably increased IL-2, IFN-gamma, and/or IL-3. The ability of these memory effector Th cells to be restimulated to secrete cytokines is maximal by 3 days after in vivo boosting with Ag, and declines rapidly thereafter. Memory effector Th are induced in the spleens of KLH-primed mice that have been depleted of precursor T cells by thymectomy more than 25 wk previously, suggesting that they are derived from a memory T cell population. Cell separation on the basis of CD45RB or MEL-14, surface markers that are down-regulated on memory CD4+ cells, indicates that memory effector Th are in the CD45RBlo and MEL-14- subsets of CD4+ T cells. The frequency of KLH-specific splenic CD4+ T cells with the capacity to secrete cytokines in limiting dilution cultures is very low in unprimed mice (1/3 x 10(4) to 1/9 x 10(4)), but increases as much as 50-fold after priming. IL-2, but not IL-4, can be detected in the supernatants of stimulated unprimed CD4+ T cells. Both IL-2- and IL-4-producing cells are readily detected after priming, and frequencies of IL-2-secreting cells (1/250 to 1/4000) are up to ninefold greater than those for IL-4 secreting cells. Boosting elicits variable (two to eightfold) increases in the frequencies of both IL-2- and IL-4-producing CD4+ T cells. However, high IL-4 titers associated with memory effector Th function can be obtained when significant frequency changes are not detected after boosting. The data suggest that reactivation of resting memory Th in vivo induces their differentiation into effector Th with the capacity to secrete much higher levels of IL-4. Although the capacity to produce high levels of IL-4 is associated with both primary and memory CD4+ effector populations, memory effector Th are the higher producers.(ABSTRACT TRUNCATED AT 400 WORDS)

Helper T cell memory: more questions than answers

The critical participation of helper T cells in immunologic memory of animals is clear. Features of antigen-specific CD4 memory cells in primed animals that distinguish them from naive cells are their increased frequency, their ability to secrete lymphokines in addition to IL-2 and their expression of distinct arrays of surface molecules. The latter include increased CD44, CD45RO, LFA-3 and VLA-4 and decreased CD45RA,B and Mel-14. These differences in surface markers may contribute to increased interaction potential for APC, and to distinct patterns of recirculation, but direct demonstrations of the former have yet to be provided. Other possible distinctions that are also largely hypothetical, include distinct requirements for activation and the ability to respond more rapidly to stimulation. The factors that regulate the development of memory helper T cells are also unknown.

Long-term CD4+ memory T cells from the spleen lack MEL-14, the lymph node homing receptor

We have characterized the surface phenotype and function of long-lived, Ag-specific memory CD4+ T cells generated in vivo by immunization with keyhole limpet hemocyanin (KLH). CD4+ T cells from the spleens of mice primed more than 2 mo previously with KLH, produced high levels of IL-2 and IL-3, and low levels of IL-4 and IFN-gamma in response to in vitro restimulation with specific Ag. The KLH-primed T cells mediated carrier-specific helper activity for the antibody production by NIP-primed B cells in secondary in vitro responses to NIP-KLH. Subsets of CD4+ T cells from KLH-primed mice were isolated on the basis of surface CD45RB (23G2) by magnetic separation and were examined for functional capacity in several assays of Ag-specific recall. Virtually all of the secretion of IL-2, IL-3, IL-4, and IFN-gamma in response to restimulation with Ag in vitro was associated with, and considerably enriched in, the CD45RB- subset of CD4+ T cells. Similarly, carrier-specific helper function and Ag-specific proliferation in vitro were also confined to the CD45RB-, CD4+ subset of T cells, confirming the previous association of this surface phenotype with memory Th cell activity. We also examined expression of the lymphocyte homing receptor, MEL-14 (gp90MEL), which is required for lymphocyte extravasation to peripheral lymph nodes and is present in high levels on naive T cells. MEL-14 positive and negative subsets of CD4+ T cells from long term KLH-primed mice were evaluated for Ag-specific memory function in terms of lymphokine production, Ag-induced proliferation, and helper activity. Each of these functions was associated exclusively with the MEL-14- subset of CD4+ T cells, which exhibited responses comparable to the CD45RB- subset. These data indicate that memory Th cell function in the spleen is contained within the MEL-14-, CD45RB- subset of CD4+ T cells and suggest that memory helper cells may have different patterns of recirculation from naive T cells.

Long-term CD4+ memory T cells from the spleen lack MEL-14, the lymph node homing receptor

We have characterized the surface phenotype and function of long-lived, Ag-specific memory CD4+ T cells generated in vivo by immunization with keyhole limpet hemocyanin (KLH). CD4+ T cells from the spleens of mice primed more than 2 mo previously with KLH, produced high levels of IL-2 and IL-3, and low levels of IL-4 and IFN-gamma in response to in vitro restimulation with specific Ag. The KLH-primed T cells mediated carrier-specific helper activity for the antibody production by NIP-primed B cells in secondary in vitro responses to NIP-KLH. Subsets of CD4+ T cells from KLH-primed mice were isolated on the basis of surface CD45RB (23G2) by magnetic separation and were examined for functional capacity in several assays of Ag-specific recall. Virtually all of the secretion of IL-2, IL-3, IL-4, and IFN-gamma in response to restimulation with Ag in vitro was associated with, and considerably enriched in, the CD45RB- subset of CD4+ T cells. Similarly, carrier-specific helper function and Ag-specific proliferation in vitro were also confined to the CD45RB-, CD4+ subset of T cells, confirming the previous association of this surface phenotype with memory Th cell activity. We also examined expression of the lymphocyte homing receptor, MEL-14 (gp90MEL), which is required for lymphocyte extravasation to peripheral lymph nodes and is present in high levels on naive T cells. MEL-14 positive and negative subsets of CD4+ T cells from long term KLH-primed mice were evaluated for Ag-specific memory function in terms of lymphokine production, Ag-induced proliferation, and helper activity. Each of these functions was associated exclusively with the MEL-14- subset of CD4+ T cells, which exhibited responses comparable to the CD45RB- subset. These data indicate that memory Th cell function in the spleen is contained within the MEL-14-, CD45RB- subset of CD4+ T cells and suggest that memory helper cells may have different patterns of recirculation from naive T cells.

Cardiovascular effects of platelet-activating factor

Sudden release of platelet-activating factor (PAF) into the circulation can cause hypotension, tachycardia, and circulatory collapse. To further examine this response, we performed detailed studies of cardiovascular function after PAF administration to young domestic pigs and newborn piglets. Our results indicate that circulatory dysfunction after PAF reflects severe constriction of pulmonary resistance vessels and consequent acute right ventricular failure. Although PAF-induced coronary artery constriction and contractile depression may be complicating problems, left ventricular underperfusion and dysfunction after PAF are mainly the result of systemic arterial hypotension and diminished left ventricular filling. The adverse hemodynamic effects of PAF are accompanied by substantial release of thromboxane A2 (TxA2). These effects are mimicked by the TxA2 agonist U-46619 and partially blocked by specific and nonspecific inhibitors of TxA2 synthesis (OKY-046 and indomethacin). Even more potent blockade of PAF action is exerted by the TxA2 receptor blocker, SQ 29,548. Taken together, these findings indicate that severe pulmonary vascular constriction and hemodynamic collapse soon after intravenous PAF are at least partially mediated by PAF-induced TxA2 release. Tachyphylaxis to PAF influence has been observed in studies of leukocyte and platelet function. We hypothesized that tachyphylaxis to PAF might also occur in our studies of constrictor responses in pulmonary vessels. Recently, we have examined the capacity of PAF to produce sustained pulmonary vasoconstriction in open-chested, anesthetized newborn piglets. Infusions sufficient to produce 100% increase in mean pulmonary artery pressure after 3 min showed no loss of efficacy when sustained for 30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Helper T-cell subsets: phenotype, function and the role of lymphokines in regulating their development

We have concentrated here on the lymphokines which might serve to regulate the different pathways of precursor development. We suggest that, as a result of antigenic stimulation, specific precursor cells both proliferate and become committed to develop into either an effector cell, a memory cell or an anergized cell. Anergy has not been dealt with in this review, but it is likely to be one of the options available. The development of an effector population takes 4-7 d (quite analogous to the time it takes for CTLp to become CTL and for resting B to become Ab-forming cells). The effector populations are large, generally IL-2R-positive cells. These cells have upregulated many adhesion molecule systems [e.g., Pgp-1, LFA-1 and ICAM-1 (Swain unpublished)], but downregulated the Mel-14 homing receptor. Effectors are ready to respond to APC such as specific B cells with a rapid synthesis and secretion of lymphokines. The effector population is then quickly downregulated, both by the turn off of lymphokine synthesis/secretion and possibly by its own suicide. This kind of pattern makes teleological sense since the cells making such high titers of lymphokines could have many potent pleitropic effects. It also seems to be the strategy employed in the generation of other terminally differentiated effectors (such as CTL and plasma cells). The requirement for restimulation and the requirement for direct and perhaps prolonged contact between the helper effector and the APC-B cell can be expected to help ensure that these lymphokines are localized (reviewed in Swain & Dutton 1987, Swain & Croft 1990) and effectively delivered to specific responding cells. We postulate that at the same time, or perhaps subsequent to this, another set of signals drives precursors to generate prememory cells. Our studies suggest these emerging memory cells may be phenotypically unique and we postulate that they are specialized to become a "long-lived" population of memory cells that will persist indefinitely as a protective population of increased frequency for the antigen encountered and which is also able to respond more rapidly and effectively. The greater effectiveness of the memory response would thus be due to dramatically increased frequency, to characteristic and stable changes in adhesion molecule expression and to the fact that, in addition to IL-2, resting memory cells also secrete at least low titers of IL-3, IL-4, IFN-gamma and other lymphokines upon initial restimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Sustained effects of platelet-activating factor infusion in piglets

Acute exposure to platelet-activating factor (PAF) causes severe pulmonary vasoconstriction (PV), but its action may be markedly limited by tachyphylaxis. To determine the effects of PAF exposure per se and the effects compared with the hypoxemic state (33 +/- 1 mm Hg), PAF infusions (0.05-0.15 nmol/kg/min x 30-180 min) were administered to 15 open-chested, anesthetized, neonatal piglets before and during administration of selective receptor blockers to PAF (SRI 63,441, 5 mg/kg i.v. or WEB 2086, 10 mg/kg i.v.) or vehicle. Measurements included mean pulmonary (PAP) and systemic arterial pressures, cardiac index, right and left ventricular pressures and dimensions, and coronary blood flow. Mean PAP and pulmonary vascular resistance index rose in response to 30 min PAF infusion (14 +/- 1 to 30 +/- 1 mm Hg and 4500 +/- 700 to 16,400 +/- 1900 dynes s cm-5.kg, both p less than 0.01, n = 10). Similar changes occurred when PAF was infused for 180 min (n = 5). Other parameters were unaffected. Acute hypoxia also increased in PAP and pulmonary vascular resistance index (17 +/- 1 to 32 +/- 2 mm Hg and 6400 +/- 900 to 17,100 +/- 1800 dynes s cm-5.kg, both p less than 0.01) and did not alter other measured variables. Treatment with SRI 63,441 prevented PAF-induced increases in PAP (14 +/- 1 to 14 +/- 1 mm Hg, p less than 0.05) and pulmonary vascular resistance index (5300 +/- 900 to 5500 +/- 800 dynes s cm-5.kg, p less than 0.05) but failed to alter the response to hypoxia. SRI 63,441 and WEB 2086, administered during PAF infusion, rapidly reversed PAF action. Vehicle had no effect. We conclude that PAF can produce severe and sustained PV in vivo and that PAF receptor blockade may be useful in treatment of neonatal disease featuring PAF-mediated PV. PAF receptors may not be involved in PV induced by hypoxia.

Characterization of antigen-specific CD4+ effector T cells in vivo: immunization results in a transient population of MEL-14-, CD45RB- helper cells that secretes interleukin 2 (IL-2), IL-3, IL-4, and interferon gamma

In previous studies we demonstrated that, following activation by mitogens or alloantigens, helper T cell precursors proliferate and differentiate in vitro to produce a population of effector cells that secrete high titers of lymphokines upon restimulation. In this report, we demonstrate that a similar effector population develops in vivo following primary antigen stimulation. When restimulated with specific antigen in vitro, CD4+ T cells from mice primed 5 to 7 days previously by subcutaneous administration of keyhole limpet hemocyanin (KLH) in adjuvant, produced high levels of interleukin 2 (IL-2), IL-4, and IL-3, and little or no interferon gamma (IFN-gamma) or IL-5. The effector T cells provided excellent helper activity for in vitro antibody responses of 4-hydroxy-5-iodo-nitrophenyl acetic acid-primed B cells with the production principally of the immunoglobulin G1 (IgG1) and IgM isotypes, small quantities of IgG3, and no detectable IgG2a, or IgG2b. Antigen-specific secretion of IL-2, IL-3, and IL-4 by in vivo effectors was detectable by 12 hours following in vitro restimulation. IFN-gamma and IL-5 were not detected until 48 and 72 hours of culture, respectively, and low levels of these lymphokines were produced. Lymphokine production by primed CD4+ T cells could be induced as early as 3 days following immunization, peaked on day 5, and declined thereafter. The kinetics of in vivo appearance of effector CD4+ T cells that produce lymphokines upon restimulation in vitro were similar for each of the lymphokines examined. Mice depleted of precursor CD4+ T cells by adult thymectomy exhibited limited capacity to generate lymphokine secreting CD4+ T cells in response to primary immunization with KLH, suggesting that the majority of lymphokine producing T cells arise from short-lived and/or precursor cells. Separation of CD4+ T cells from KLH-primed mice on the basis of expression of the lymph node-specific homing receptor, MEL-14, revealed that antigen-specific production of IL-2, IL-3, IL-4, and IFN-gamma was exclusively associated with the MEL-14- subset of CD4+ T cells. Separation on the basis of CD45RB expression, demonstrated that antigen-specific lymphokine production was primarily associated with the minor CD45RB- population, which has been previously associated with memory activity. Our results indicate that primary in vivo immunization leads to the development of a transient population of helper-effectors with a unique phenotype that can produce large quantities of lymphokines and mediate excellent helper activity for B cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Circulatory effects of endothelin in newborn piglets

Endothelin, a recently described endothelial cell-derived peptide, produces pulmonary and coronary vasoconstriction in mature animals. We investigated the acute hemodynamic effects of porcine endothelin in 14 anesthetized open-chest new-born piglets during normoxia (Pao2 = 102 +/- 5 mmHg) and hypoxia (fractional inspired O2 concentration = 0.12 X 15 min, Pao2 = 31 +/- 1 mmHg). Six of these animals were pretreated with indomethacin, a cyclooxygenase inhibitor. Low-dose (100 pmol/kg) intravenous bolus injection of endothelin decreased pulmonary vascular resistance index (PVRI) (42 +/- 6 to 16 +/- 4 mmHg.l-1.min.kg, P less than 0.01) and increased coronary blood flow (CBF) (17 +/- 2%, P less than 0.01); cardiac index (CI) and coronary vascular resistance were unaffected. The pulmonary and coronary responses to endothelin were preserved during hypoxia: PVRI fell (160 +/- 22 to 83 +/- 13 mmHg.l-1.min.kg, P less than 0.05) and CBF rose (35 +/- 11%, P less than 0.05). Low-dose endothelin moderately increased mean arterial pressure (61 +/- 3 to 75 +/- 6 mmHg, P less than 0.05) and systemic vascular resistance index (SVRI) (375 +/- 23 to 491 +/- 41 mmHg.l-1.min.kg, P less than 0.01). High-dose (1,000 pmol/kg) endothelin mildly decreased PVRI (51 +/- 7 to 35 +/- 12, NS), moderately increased SVRI (375 +/- 45 to 594 +/- 95 mmHg.l-1.min.kg, P less than 0.05), and markedly diminished CBF (-54 +/- 6%, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of thromboxane A2 receptor antagonism on pulmonary vasoconstrictor responses

Thromboxane A2 (TxA2) is an arachidonic acid metabolite which causes severe pulmonary vasoconstriction (PV) and may mediate the PV produced by platelet-activating factor (PAF-acether) and leukotriene D4 (LTD4). To determine the role of TxA2 receptors on PAF-acether, LTD4, and hypoxia-induced PV, we administered PAF-acether 0.1 nmol/kg, the TxA2 analog U-46619 0.2 micrograms/kg/min, LTD4 3.0 micrograms/kg, or acute hypoxia (FiO2 = 0.12 for 3 min) before and during the infusion of the selective TxA2 receptor blocker SQ 29,548 50 micrograms/kg/min or vehicle into 27 open-chest, anesthetized newborn piglets, measuring pulmonary and systemic arterial pressures, cardiac index, and right and left ventricular pressures and dimensions. Mean pulmonary arterial pressure rose and cardiac index fell in response to PAF-acether (14 +/- 1 to 32 +/- 2 mm Hg and 91 +/- 5 to 15 +/- 5 mL/kg/min, both p less than 0.01), U-46619 (11 +/- 1 to 28 +/- 2 mm Hg and 93 +/- 10 to 36 +/- 9 mL/kg/min, both p less than 0.01), and LTD4 (13 +/- 3 to 22 +/- 2 mm Hg and 85 +/- 12 to 29 +/- 9 mL/kg/min, both p less than 0.05). Acute hypoxia increased PAP (12 +/- 1 to 26 +/- 2 mm Hg, p less than 0.01) but did not alter cardiac index. Infusion of SQ 29,548 prevented PAF-acether and U-46619-induced increases in pulmonary arterial pressure (13 +/- 1 to 14 +/- 1 mm Hg and 12 +/- 1 to 12 +/- 1 mm Hg) and decreases in cardiac index (70 +/- 4 to 70 +/- 3 mL/kg/min and 94 +/- 14 to 92 +/- 12 mL/kg/min) but failed to alter the response to LTD4 or hypoxia. Vehicle had no effect. We conclude that TxA2 receptors are not involved in LTD4 or hypoxia-induced PV but play an important role in the PV produced by PAF-acether and U-46619.

Predominance of T cells that express CD45R in the CD4+ helper/inducer lymphocyte subset of neonates

Neonates have an increased risk of severe infections. For several in vitro and in vivo immune responses, neonates have been shown to have significant differences when compared to normal adults. To indirectly study immune cellular defects, we compared cell surface markers on cord blood lymphocytes (CBL) from 58 term infants to peripheral blood lymphocytes (PBL) from 17 healthy adults using flow cytometry with standard as well as newly defined monoclonal antibodies (Mab) that distinguish regulatory T cells. CBL had significantly smaller percentages of lymphocytes that express the CD2 and CD8 markers (total T cells, and suppressor/cytotoxic T cells, respectively), although absolute numbers of CD2+ and CD8+ cells were comparable in neonates and adults. CBL and PBL were similar in terms of the percentage of CD4+ cells (helper/inducer T cells), although the absolute numbers of CD4+ cells were higher in CBL than in PBL. The CD4+ population was subdivided into cells bearing the virgin and memory T cell phenotypes using anti-2H4 and anti-4B4 Mab and dual parameter analysis with anti-CD4. Neonates were deficient in the percentage of CD4+, 4B4+ (3.8 +/- 2.8 vs 13.4 +/- 7.5, P less than 0.001), but equivalent to adults in the percentage of CD4+, 2H4+ T cells (21.4 +/- 9.8 vs 18.8 +/- 12.8). In absolute numbers, neonates had fewer CD4+, 4B4+ cells (178 +/- 173 vs 344 +/- 152 cells/microliters, P less than 0.001), but more CD4+,2H4+ cells (978 +/- 572 vs 542 +/- 518 cells/microliters, P less than 0.01) than adults. The predominance of 2H4+ virgin T cells in the CD4 population whose function is associated with that of the induction of suppression rather than the up-regulation of immune responses may contribute to the observed susceptibility of neonates to infection.

Circulatory effects of PAF-acether in newborn piglets

Platelet-activating factor (PAF-acether) is a lipid mediator that can exhibit potent vasoconstrictor influence in the pulmonary vessels. Therefore, the release of PAF-acether during inflammatory conditions in newborns might cause deleterious increases in pulmonary vascular tone. Thirty-four anesthetized open-chest newborn piglets were given 0.01-1 nmol PAF-acether iv. In separate experiments, animals were untreated or treated with either indomethacin (a cyclooxygenase inhibitor), SQ 29548 (a thromboxane receptor blocker), or LY 171883 (a leukotriene receptor blocker). The primary hemodynamic change was a 67 to 1,537% increase in the pulmonary vascular resistance index (PVRI) (P less than 0.01): mean pulmonary artery pressure (PAP) rose significantly at all doses tested, whereas only the largest dose consistently decreased cardiac index. Treatment with indomethacin or SQ 29548 prevented the decrease in cardiac index and attenuated the PAF-acether-induced rises in PAP and PVRI. Vehicle and LY 171883 had no effect. The inhibitory influence of indomethacin and SQ 29548 suggests that an important component of PAF-acether's pulmonary vasoconstrictor action is mediated (at least in the newborn piglet) by cyclooxygenase products, most likely thromboxane.

Flow cytometric analysis of I-J expression on murine bone marrow-derived macrophages

Attempts to analyze bone marrow-derived macrophages (BMDM) by flow cytometry have been prohibited because of their high autofluorescence. Using an autofluorescence reduction method of Steinkamp and Stewart to reduce the autofluorescence of BMDM, we were able to examine several macrophage populations for their expression of I-A, I-J, and Mac-1 cell surface determinants. Bone marrow cells examined immediately after removal from the femur contain 50-60% Mac 1-positive cells (mainly granulocytes). During the next few days granulocytes and nonmacrophage precursor cells die, and the number of Mac 1-positive cells decrease. Once the bone marrow cells have been maintained in L cell conditioned medium (LCM) for 2 to 3 days, the number of cells expressing Mac 1 increases rapidly from 20% to 98% during the next 3 to 4 days. Bone marrow cells grown in LCM do not express I-J until these cells have been in culture 3 to 4 days, and the number of cells expressing I-J (up to 90% positive) parallels the increase in macrophages. Bone marrow cells maintained in LCM did not express detectable I-A during the 14 days these cells were examined. Two other macrophage populations often used in a variety of immunological studies were analyzed by flow cytometry. We found that the majority (up to 80%) of peritoneal cells expressed I-A, and only 20% of peritoneal cells had I-J cell surface determinants. On the other hand, peritoneal exudate cells collected 4 days after thioglycolate medium treatment were predominantly I-J positive (up to 70%), and only about 30% of these cells expressed I-A cell surface antigens. The binding of anti-I-J IgM antibody to BMDM was not to Fc receptors because pretreating these cells with up to 25 micrograms of an IgG2a myeloma protein did not block anti-I-J antibody binding. The addition of 25-200 micrograms of monoclonal anti-Fc receptor antibody was also ineffective in blocking the binding of a monoclonal anti-I-Jk antibody to BMDM. Pretreatment of BMDM with the IgM fraction of several control IgM antibody preparations did not block the specific binding of fluoresceinated anti-I-J IgM antibody. BMDM provide a pure population of macrophages that express a significant level of cell surface I-J antigens. Bone marrow cells grown in LCM are essentially devoid of other contaminating cells, and the increase in the number of I-J-positive cells parallels the increase in macrophages in these cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of macrophages in anti-idiotypic antibody and T suppressor factor induction of timothy grass pollen antigen B-specific T suppressor cells

Cultures of normal spleen cells with anti-idiotypic antibody (anti-Id) or antigen B (AgB)-specific T suppressor factor (Tsf1) in mini-Marbrook chambers for 4 days at 37 degrees C lead to the in vitro induction of AgB-specific T suppressor (TS) cells. These TS cells significantly suppress a secondary AgB-specific IgE response, but they do not affect a secondary AgB-specific IgG response. Depletion of both B cells and macrophages from normal spleen cells by panning on anti-Ig-coated petri dishes provides an enriched T cell population. These enriched T cells when cultured with anti-Id or Tsf1 in mini-Marbrook chambers do not produce AgB-specific TS cells, and mice treated with cells harvested from the mini-Marbrook chambers have normal secondary AgB-specific IgG and IgE responses. The addition of as few as 1000 bone marrow-derived macrophages (BMDM) to cultures of the enriched T cells with anti-Id, or Tsf1 restores the ability of these cultures to produce significant levels of AgB-specific TS cells. Further studies reveal that the macrophage population must be histocompatible and express a cell surface I-J antigen. Attempts to pulse BMDM with anti-Id or Tsf1 at 4 degrees C and to culture in mini-Marbrook chambers 10(3) pulsed BMDM with enriched T cells were unsuccessful in producing AgB-specific TS cells. However, pulsing BMDM with anti-Id or Tsf1 at 37 degrees C, and adding 10(3) of these pulsed BMDM to enriched T cells in culture led to the formation of significant levels of AgB-specific TS cells.