Decreased expression of IL-2 in central and effector CD4 memory cells during progression to AIDS in rhesus macaques

OBJECTIVE

HIV-1 infection in humans has been reported to lead to a shift in the cytokine balance, with a relative decrease in T helper 1 type cytokines, especially IL-2. On the basis of the expression of CD45RA, in combination with homing markers CD62L or alpha4beta7, T helper cells can be sub-divided into naive, activated naive, central memory and effector memory cells as well as gut-homing subpopulations. In addition, each subset may have the potential to express distinct cytokines. At present it is unclear whether the changes in cytokine expression observed in HIV-1-infected individuals are secondary to changes within the composition of CD4 T cell subsets or are caused by changes in cytokine expression within each subset.

MATERIALS AND METHODS

A new technique was developed to detect cytokine expression in phorbol 12-myristate 13-acetate/ionomycin-activated CD62L and alpha4beta7-expressing CD4 T cell subsets, using the protease inhibitor KD-IX-73-4.

RESULTS

In SIV-infected macaques that develop AIDS a marked decrease in IL-2 expression was found within central, effector, or gut-homing memory cell subsets, whereas the expression of IL-2 in naive T cell subsets remained unaffected. This reduced IL-2 expression by memory cells and not a loss of the frequency of CD4 memory cells accounted for the reduced expression of IL-2 by CD4 T cells during SIV infection.

CONCLUSION

As defined by the cell surface markers utilized, it appears that progression to AIDS is associated with functional impairment of memory cells, but not changes in lymphocyte circulation patterns.

Decreased HIV-specific CD4 T cell proliferation in long-term HIV-infected individuals on antiretroviral therapy

The effect of highly active antiretroviral therapy (HAART) on HIV-specific CD4 T cell proliferation in long-term HIV-infected individuals was studied. Subjects receiving treatment for over a year were compared with individuals not receiving therapy. The absolute number of HIV-specific memory CD4 T cells proliferating in response to HIV antigen was substantially higher in untreated subjects than in those on HAART. A decrease in HIV-specific memory CD4 T cells could explain the rebound in HIV replication after the termination of HAART.

CD4(+)CD8(dim) T lymphocytes exhibit enhanced cytokine expression, proliferation and cytotoxic activity in response to HCMV and HIV-1 antigens

CD4(+)CD8(dim) T cells represent a minor subset of the total CD3(+) T cell population in peripheral blood. Although transient and persistent expansions of these cells have been reported in both healthy and diseased individuals, the functional properties of the CD4(+)CD8(dim) population are largely unknown. In this study, we examined antigen-specific cytokine and proliferative responses of the CD4(+)CD8(dim) subset. In whole blood cultures stimulated with the viral antigens HCMV and HIV-1, a significant fraction of the CD4(+)CD8(dim) subset exhibited cytokine expression and proliferation in response to antigen activation. Typically, the CD4(+)CD8(dim) population contained two- to eightfold higher frequencies of antigen-specific cytokine producing cells than the CD4(+)CD8(-) population. Phenotypic analysis of the cytokine expressing CD4(+)CD8(dim) population indicated that these cells are memory T cells, with a high frequency of this population expressing the cytotoxic markers CD56 and perforin. Furthermore, the CD4(+)CD8(dim) cytokine responses to CMV were shown to be MHC class II dependent. Significantly, purified CD4(+)CD8(dim) T cells were found to possess higher CMV-specific cytotoxic activity than purified CD4(+)CD8(-) T cells in a standard (51)Cr-release CTL assay. Thus, CD4(+)CD8(dim) T cells appear to be MHC class II dependent, are capable of cytolytic effector activity, and are highly enriched within the CD4(+) cell populations specific for HCMV and HIV-1.

Use of overlapping peptide mixtures as antigens for cytokine flow cytometry

Intracellular cytokine staining and flow cytometry can be used to measure T-cell responses to defined antigens. Although CD8+ T-cell responses to soluble proteins are inefficiently detected by this approach, peptides can be used as antigens. Using overlapping peptides spanning an entire protein sequence, CD8+ T-cell responses can be detected to multiple epitopes, regardless of HLA type. In this study, overlapping peptide mixes of various lengths were compared and 15 amino acid peptides with 11 amino acid overlaps were found to stimulate both CD4+ and CD8+ T-cell responses. Such peptide mixes stimulated CD4+ T-cell responses equivalent to those observed with whole recombinant protein, while simultaneously stimulating CD8+ T-cell responses much higher than those observed with whole protein. Although 8-12 amino acid peptides produced the highest level of CD8+ T-cell responses, 15 amino acid peptides were still very effective. Peptides that were 20 amino acids in length, however, did not stimulate strong CD8+ T-cell responses at the same peptide dose. The cytokine responses to individual epitopes added up approximately to the response to the entire mix, demonstrating that large mixes can detect responses in a quantitative fashion. Unlike whole protein antigens, peptide mixes were effective at stimulating responses in both cryopreserved PBMC and blood stored for 24 h at room temperature. Thus, overlapping 15 amino acid peptide mixes may facilitate the analysis of antigen-specific CD4+ and CD8+ T-cell responses by cytokine flow cytometry, using clinical specimens that include shipped blood or cryopreserved PBMC.

Direct functional analysis of epitope-specific CD8+ T cells in peripheral blood

The functional status of virus-specific CD8+ T cells is important for the outcome and the immunopathogenesis of viral infections. We have developed an assay for the direct functional analysis of antigen-specific CD8+ T cells, which does not require prolonged in vitro cultivation and amplification of T cells. Whole blood samples were incubated with peptide antigens for <5 h, followed by staining with peptide-MHC tetramers to identify epitope-specific T cells. The cells were also stained for the activation marker CD69 or for the production of cytokines such as interferon-gamma (IFNgamma) or tumor necrosis factor-alpha (TNFalpha). With the combined staining with tetramer and antibodies to CD69 or cytokines the number of antigen-specific CD8+ T cells as well as the functional response of each individual cell to the cognate antigen can be determined in a single experiment. Virus-specific CD8+ T cells that are nonfunctional, as well as those that are functional under the same stimulating conditions can be simultaneously detected with this assay, which is not possible by using other T-cell functional assays including cytotoxicity assay, intracellular cytokine staining, and enzyme-linked immunospot (ELISPOT) assay.

Clonotypic structure of the human CD4+ memory T cell response to cytomegalovirus

High steady-state frequencies of CMV-specific CD4(+) memory T cells are maintained in CMV-exposed subjects, and these cells are thought to play a key role in the immunologic control of this permanent infection. However, the essential components of this response are poorly defined. Here, we report the use of a step-wise application of flow cytometric and molecular techniques to determine the number and size of the TCR Vbeta-defined clonotypes within freshly obtained CMV-specific CD4(+) memory T cell populations of four healthy, CMV-exposed human subjects. This analysis revealed a stable clonotypic hierarchy in which 1-3 dominant clonotypes are maintained in concert with more numerous subdominant and minor clonotypes. These dominant clonotypes accounted for 10-50% of the overall CMV response, and comprised from 0.3 to 4.0% of peripheral blood CD4(+) T cells. Two subjects displayed immunodominant responses to single epitopes within the CMV matrix phosphoprotein pp65; these single epitope responses were mediated by a single dominant clonotype in one subject, and by multiple subdominant and minor clonotypes in the other. Thus, the CMV-specific CD4(+) T cell memory repertoire in normal subjects is characterized by striking clonotypic dominance and the potential for epitope focusing, suggesting that primary responsibility for immunosurveillance against CMV reactivation rests with a handful of clones recognizing a limited array of CMV determinants. These data have important implications for the understanding of mechanisms by which a genetically stable chronic viral pathogen such as CMV is controlled, and offer possible insight into the failure of such control for a genetically flexible pathogen like HIV-1.

CD4(+)CD8(dim) T lymphocytes exhibit enhanced cytokine expression, proliferation and cytotoxic activity in response to HCMV and HIV-1 antigens

CD4(+)CD8(dim) T cells represent a minor subset of the total CD3(+) T cell population in peripheral blood. Although transient and persistent expansions of these cells have been reported in both healthy and diseased individuals, the functional properties of the CD4(+)CD8(dim) population are largely unknown. In this study, we examined antigen-specific cytokine and proliferative responses of the CD4(+)CD8(dim) subset. In whole blood cultures stimulated with the viral antigens HCMV and HIV-1, a significant fraction of the CD4(+)CD8(dim) subset exhibited cytokine expression and proliferation in response to antigen activation. Typically, the CD4(+)CD8(dim) population contained two- to eightfold higher frequencies of antigen-specific cytokine producing cells than the CD4(+)CD8(-) population. Phenotypic analysis of the cytokine expressing CD4(+)CD8(dim) population indicated that these cells are memory T cells, with a high frequency of this population expressing the cytotoxic markers CD56 and perforin. Furthermore, the CD4(+)CD8(dim) cytokine responses to CMV were shown to be MHC class II dependent. Significantly, purified CD4(+)CD8(dim) T cells were found to possess higher CMV-specific cytotoxic activity than purified CD4(+)CD8(-) T cells in a standard (51)Cr-release CTL assay. Thus, CD4(+)CD8(dim) T cells appear to be MHC class II dependent, are capable of cytolytic effector activity, and are highly enriched within the CD4(+) cell populations specific for HCMV and HIV-1.

Factors affecting the efficiency of CD8+ T cell cross-priming with exogenous antigens

Processing of exogenous protein Ags by APC leads predominantly to presentation of peptides on class II MHC and, thus, stimulation of CD4+ T cell responses. However, "cross-priming" can also occur, whereby peptides derived from exogenous Ags become displayed on class I MHC molecules and stimulate CD8+ T cell responses. We compared the efficiency of cross-priming with exogenous proteins to use of peptide Ags in human whole blood using a flow cytometry assay to detect T cell intracellular cytokine production. CD8+ T cell responses to whole CMV proteins were poorly detected (compared with peptide responses) in most CMV-seropositive donors. Such responses could be increased by using higher doses of Ag than were required to achieve maximal CD4+ T cell responses. A minority of donors displayed significantly more efficient CD8+ T cell responses to whole protein, even at low Ag doses. These responses were MHC class I-restricted and dependent upon proteosomal processing, indicating that they were indeed due to cross-priming. The ability to efficiently cross-prime was not a function of the number of dendritic cells in the donor's blood. Neither supplementation of freshly isolated dendritic cells nor use of cultured, Ag-pulsed dendritic cells could significantly boost CD8 responses to whole-protein Ags in poorly cross-priming donors. Interestingly, freshly isolated monocytes performed almost as well as dendritic cells in inducing CD8 responses via cross-priming. In conclusion, the efficiency of cross-priming appears to be poor in most donors and is dependent upon properties of the individual's APC and/or T cell repertoire. It remains unknown whether cross-priming ability translates into any clinical advantage in ability to induce CD8+ T cell responses to foreign Ags.

Gamma interferon expression in CD8(+) T cells is a marker for circulating cytotoxic T lymphocytes that recognize an HLA A2-restricted epitope of human cytomegalovirus phosphoprotein pp65

Antigen-specific CD8(+) T cells with cytotoxic activity are often critical in immune responses to infectious pathogens. To determine whether gamma interferon (IFN-gamma) expression is a surrogate marker for cytotoxic T lymphocytes (CTL), human cytomegalovirus-specific CTL responses were correlated with CD8(+) T-cell IFN-gamma expression determined by cytokine flow cytometry. A strong positive correlation was observed between specific lysis of peptide-pulsed targets in a (51)Cr release assay and frequencies of peptide-activated CD8(+) T cells expressing IFN-gamma at 6 h (r(2) = 0.72) or 7 days (r(2) = 0.91). Enumeration of responding cells expressing perforin, another marker associated with CTL, did not improve this correlation. These results demonstrate that IFN-gamma expression can be a functional surrogate for identification of CTL precursor cells.

Immunofluorescence analysis of T-cell responses in health and disease

The use of flow cytometry to study the functional responses of T cells by immunofluorescent staining for intracellular cytokines and other markers is a growing field of clinical interest. In this article, we describe methods for the rapid evaluation of T-cell responses to mitogens and specific antigens and explore how these assays might be valuable in various clinical settings.

The CD4(+) T cell response to HIV-1

Although virus-specific CD4(+) T cells have proven to be a critical component of the immunologic control of chronic viral infections in a number of models, the role and even the existence of HIV-1-specific CD4(+) T cells in human HIV-1 infection has been controversial. Recent advances in quantifying and functionally characterizing HIV-1-specific T cells may shed light on the participation of these cells in anti-HIV-1 host defense.

Assessment of donor T-cell function in cellular blood components by the CD69 induction assay: effects of storage, gamma radiation, and photochemical treatment

BACKGROUND

Functional donor T-lymphocytes in blood components may cause a variety of transfusion complications. A flow cytometric assay based on the measurement of induced CD69 expression may be an alternative to cell proliferation methods in determining the functional status of these cells in blood components.

STUDY DESIGN AND METHODS

Seven units of whole blood, RBCs, and platelet concentrates (PCs) were stored under blood bank conditions. Half of 3 PCs each were gamma-radiated or treated with UVA+psoralen; the other half served as controls. Samples were analyzed for phorbolester-induced expression of CD69 as an indicator of cell responsiveness and for exclusion of propidium iodide as a measure of cell membrane integrity and viability.

RESULTS

CD69 inducibility and propidium iodide exclusion decreased exponentially (half-life, 3. 3 and 8.1 days, respectively) during cold blood storage. Irradiation and UVA+psoralen treatment of PCs immediately reduced CD69 inducibility to 21 percent (controls, 82%; p = 0.004) and 12 percent (controls, 95%; p = 0.0008), respectively. The proportion of cells capable of propidium iodide exclusion was similar in treated samples and controls, but it declined faster in the treated samples during subsequent storage.

CONCLUSION

Flow cytometric measurement of CD69 induction can be adapted to provide quantitative assessment of T-cell function in blood components. Results obtained by the CD69 assay are in general agreement with those previously reported by use of proliferation methods; the assay may be useful for special applications in transfusion medicine.

Enhancement of HIV type 1 antigen-specific CD4+ T cell memory in subjects with chronic HIV type 1 infection receiving an HIV type 1 immunogen

We examined HIV-1 specific memory helper T immune responses in chronically HIV-infected subjects who received an immune-based therapy (HIV-1 immunogen, Remune). Subjects in this study exhibited significant increases (p < 0.05) in the frequency of helper T memory cells expressing interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) in response to HIV-1 antigens in vitro. The frequencies of HIV-specific memory T cells increased after successive immunizations and exhibited a correlation with the standard tritiated thymidine incorporation lymphocyte proliferation assay (r = 0.72, p < 0.0008). These results support the notion that HIV-specific memory immune responses can be stimulated in subjects with chronic HIV infection. Further investigations are warranted to determine whether the induction of such responses is associated with virologic control.

Flow cytometric measurement of intracellular cytokines detects immune responses in MUC1 immunotherapy

The detection of tumor-specific T cells in immunized cancer patients usually relies on lengthy and difficult CTL assays; we now report on flow cytometry to detect the intracellular cytokines interleukin 2 (IL-2), IL-4, IFN-gamma, and tumor necrosis factor alpha (TNF-alpha) produced by CD4+CD69+ and CD8+CD69+ activated T cells after MUC1 antigen stimulation. Peripheral blood mononuclear cells were obtained from 12 patients with adenocarcinoma injected with mannan-MUC1; cells were exposed in vitro for 18 h to MUCI peptide in the presence of CD28 monoclonal antibody and Brefeldin; permeabilized cells were used for the expression of cytokines. After stimulation in vitro with MUC1-variable number of tandem repeats peptides, CD8+CD69+ T cells from all immunized patients generated 3-9 times higher levels of TNF-alpha(P < 0.038) and IFN-gamma (P <0.010) than did cells from 12 normal subjects; minor increases in IL-4 occurred. By contrast, CD4+CD69+ cells showed no overall alteration in TNF-alpha and IFN-gamma cytokine production, although in some patients, their measurement was informative; the measurement of IL-2 was not useful in either CD4+CD69+ or CD8+CD69+ cells. We conclude that in MUC1-immunized patients, the measurement of TNF-alpha and IFN-gamma in activated CD69+CD8+ T cells may be indicative of their immune status.

Frequencies of memory T cells specific for varicella-zoster virus, herpes simplex virus, and cytomegalovirus by intracellular detection of cytokine expression

Memory T cells specific for varicella-zoster virus (VZV), herpes simplex virus (HSV), and human cytomegalovirus (HCMV) were compared in immune adults by intracellular cytokine (ICC) detection. The mean percentages of CD4+ T cells were 0.11% for VZV and 0.22% for HSV by interferon (IFN)-gamma production; the frequency for HCMV was significantly higher at 1.21%. Percentages of VZV-, HSV-, and HCMV-specific CD4+ T cells were similar by use of tumor necrosis factor (TNF)-alpha. HCMV-stimulated CD8+ T cells produced IFN-gamma (1.11%) and TNF-alpha (1.71%); VZV- and HSV-specific CD8+ T cells were not detectable. VZV CD4+ T cell numbers were similar in young adults with natural or vaccine-induced immunity. VZV CD4+ T cells were significantly less frequent in older adults. Secondary varicella immunization did not increase VZV-specific CD4+ T cell frequencies by ICC assay. Numbers of memory T cells specific for herpesviruses may vary with sites of viral latency and with host age.

HIV-1-specific CD4+ T cells are detectable in most individuals with active HIV-1 infection, but decline with prolonged viral suppression

The role of HIV-1-specific CD4+ T-cell responses in controlling HIV-1 infection remains unclear. Previous work has suggested that such cells are eliminated in the early stages of infection in most subjects, and thus cannot substantially contribute to host defense against HIV-1. Here, using flow cytometric detection of antigen-induced intracellular cytokines, we show that significant frequencies of gag specific, T-helper-1 CD4+ memory T cells are detectable in most subjects with active/progressive HIV-1 infection (median frequency, 0.12% of memory subset; range, 0-0.66%). Median frequencies of these cells were considerably higher in nonprogressive HIV-1 disease (0.40%), but there was substantial overlap between the two groups (range of nonprogressors, 0.10-1.7%). Continuous HIV-1 suppression with anti-retroviral therapy was associated with a time-dependent reduction in median frequencies of gag-specific CD4+ memory T cells: 0.08% in subjects treated for 4-24 weeks, and 0.03% in subjects treated for 47-112 weeks. Thus, functional HIV-1-specific CD4+ T cells are commonly available for support of anti-HIV-1 effector responses in active disease, but their decline with anti-retroviral therapy indicates that immunologic participation in long-term HIV-1 control will probably require effective vaccination strategies.

A 15-year follow-up of AJCC stage III malignant melanoma patients treated postsurgically with Newcastle disease virus (NDV) oncolysate and determination of alterations in the CD8 T cell repertoire

BACKGROUND

The development of effective adjuvant therapies for the treatment of high-risk melanoma patients is critical for the prevention of metastatic disease and improvement of patient survival. Active specific immunotherapy has been tested as an adjuvant treatment in numerous clinical trials with overall limited, but occasionally promising, success rates. Newcastle disease virus (NDV) oncolysate has been utilized as an adjunctive immunotherapeutic agent in the postsurgical management of these patients. A phase II study initiated in 1975 using adjuvant vaccine therapy composed of allogeneic and autologous human melanoma cells infected with live NDV (NDV oncolysate) in patients with AJCC stage III melanoma following therapeutic lymph node dissection has shown >60% survival rate at 10 years with no adverse effects. Continued long-term analysis of trials with promising early results as well as assessment of immunologic responses generated in these patients may result in improved therapeutic decisions for clinical trials in the future.

MATERIALS AND METHODS

We analyzed the 15-year survival of patients treated postsurgically with NDV oncolysate in the phase II study described above. In an attempt to understand the immunological effects of this treatment, we have also carried out a comprehensive analysis of the peripheral blood T cell repertoire in these patients.

RESULTS

The overall 15-year survival of this group of patients is 55%. Previous studies have suggested that improved outcome in patients undergoing immunotherapy is correlated with increased numbers of CD8(+)CD57(+) cells. In surviving patients, we observed a striking oligoclonality in the CD8(+) T cell population in peripheral blood, which reflects clonal expansions in the CD8(+)CD57(+) subset.

CONCLUSIONS

The data suggest that adjuvant vaccination with NDV oncolysates is associated with prolonged survival of patients with lymph node-positive malignant melanoma and that CD8(+) T cells may be an important component of therapeutic efficacy.

Normal human CD4+ memory T cells display broad heterogeneity in their activation threshold for cytokine synthesis

CD4+ memory T cells coordinate immune responses against viruses and other pathogens via the Ag-induced secretion of potent effector cytokines. The efficacy of these responses depends on both the overall number of pathogen-specific memory T cells and the particular array of cytokines that these cells are programmed to secrete. Here, we provide evidence that heterogeneity in Ag triggering thresholds constitutes an additional critical determinant of memory T cell function. Using a novel assay that allows single-cell detection of Ag-specific T cell cytokine production, we demonstrate that CMV-specific CD4+ memory cells from human peripheral blood display pronounced differences in their costimulatory requirements for Ag-induced triggering of IFN-gamma and IL-2 secretion, ranging from cells that trigger with little costimulation (e.g., resting APC alone) to cells requiring potent costimulation through multiple pathways (resting APC plus multiple costimulatory mAbs, or activated APC). These differences in costimulatory requirements are independent of clonal differences in TCR signaling intensity, consistent with an intrinsic activation-threshold heterogeneity that is "downstream" from the TCR. Thus, "effective" frequencies of Ag-specific CD4+ memory T cells appear to depend on the activation status of available APC, a dependence that would allow the immune system to rapidly adjust the number of functional Ag-specific memory T cells in a particular effector site according to local conditions.

Identification of functional subsets by flow cytometry: intracellular detection of cytokine expression

Methods for analysis of T cell function have traditionally relied upon measurements of proliferation or cytokine expression in bulk cultures of PBMC in long term incubations with polyclonal mitogens or putative antigen. These techniques suffer from the drawback that they do not enable analysis of single cell responses in the context of unselected cellular backgrounds. In addition these methods are not sensitive enough to rapidly assess rare event responses characteristic of cognate memory T cell responses. This review discusses recently developed flow cytometric methods designed to rapidly assess leukocyte subset cytokine responses to polyclonal activators and specific antigen in PBMC and whole blood samples. These procedures determine the percentages of activated cells and the identification of leucocyte subsets capable of expressing various cytokines and cell surface antigens. The ability to assess key intracellular functional markers by multiparameter flow cytometry offers some unique advantages in a number of clinical applications. The technical simplicity and rapidity of the flow cytometric intracellular cytokine detection techniques described in this report, as well as the widespread availability of appropriate flow cytometers and cell surface directed antibodies in clinical laboratories, suggests the possibility that this technique could be broadly applicable to the clinical evaluation of immune status. Since any cell type can be identified with this approach, responses to a variety of clinically relevant stimuli in virtually any leukocyte subset can be evaluated including monocyte responses to LPS, and T cell responses to mitogens and a variety of bacterial and viral antigens. The significance of measuring low frequency antigen-specific responses with respect to clinical significance in assessing immune status in a variety of clinical conditions and determining efficacy or immunotoxicity of drugs and vaccine antigens is discussed.

Rapid assessment of antigen induced cytokine expression in memory T cells by flow cytometry

Methods for analysis of T cell responses to specific antigen have traditionally relied on measurements of proliferation or cytokine expression in bulk cultures of PBMC in long term incubations with putative antigen. These techniques suffer from the drawback that they do not enable analysis of single cell responses in the context of unselected cellular backgrounds. It is increasingly important to not only identify cells on the basis of expression of unique surface antigens but also to determine functional and molecular parameters of individual cells in response to a variety of stimuli. We have recently developed methodologies to rapidly assess T-cell subset responses to polyclonal activators and specific antigen in whole blood. These procedures determine the percentages of activated cells and the identification of leucocyte subsets capable of expressing various cytokines and cell surface antigens. Multiparameter analysis of CD69+ /cytokine + expression in T cells in response to specific antigen (e.g. CMV, mumps) demonstrated a range of frequencies from 0.05% to 5.0% within 6 h. Frequencies of responding T cells were consistent but varied depending upon the antigen. Antigen specific T cell responses were host specific and both positively and negatively regulated by antibodies to co-receptors involved in APC-T cell interactions. These technologies will be discussed in terms of application to problems of measuring immune function parameters in disease. The modified technique described in this report is compatible with simple and rapid analysis of clinical samples and provides a means to directly examine the effects of in vivo drug concentrations on T cell immunity. Studies are in progress to examine the sensitivity of this cellular assay to drugs and other therapeutic modalities in clinical samples.

Detection of antigen-specific T cell cytokine expression in whole blood by flow cytometry

We have recently described a highly sensitive flow cytometric technique, based on the ability to detect single cell expression of cytokines, to simultaneously quantitate and phenotypically characterize antigen-specific memory/effector T cells in PBMC cultures. In this report, we describe a simplified procedural modification which enables the rapid detection of low frequency memory CD4+ and CD8+ T cells expressing cytokines in response to soluble antigen in whole blood. When compared with T cell responses in PBMC cultures, whole blood cultures demonstrated similar but slightly higher percentages of T cells responsive to specific antigen. In addition, T cell responses to cytomegalovirus in whole blood were observed only in sensitized (seropositive) individuals, and CD4+ T cell responses could be blocked by anti-class II MHC antibodies. This procedure may provide a means to examine direct effects of pharmacological drug concentrations on T cell immunity in clinical samples.

Simultaneous detection of DNA synthesis and cytokine production in staphylococcal enterotoxin B activated CD4+ T lymphocytes by flow cytometry

Assessment of T cell activation has traditionally been performed by measuring proliferation as a function of 3[H]-thymidine incorporation, or secretion of cytokines from activated peripheral blood mononuclear cells (PBMC) in culture. An alternative method for detection of proliferation at the single cell level utilizes incorporation of bromodeoxyuridine (BrdU), an analog of thymidine, into cellular DNA. After appropriate fixation and permeabilization of the cells, a monoclonal antibody (mAb) against BrdU conjugated with a fluorescent dye is employed to measure by flow cytometry the incorporated BrdU. Here, we report a flow cytometric procedure which can be used for the simultaneous detection of BrdU incorporation, activation markers such as CD69 and CD25, and intracellular cytokines in T cell subsets from activated PBMC. Our observations are consistent with the proposal that cytokine synthesis and cell proliferation occur sequentially in CD4+ T cells stimulated with the superantigen staphylococcal enterotoxin B (SEB). The majority of cells expressing the cytokines IFN-gamma and IL-2 at 48 h appear to have undergone DNA synthesis, however all proliferating cells do not express IFN-gamma or IL-2. The methods presented in this report offer a unique approach for studying simultaneous expression of key cellular activation events in phenotypically resolved lymphocyte populations.

Determination of antigen-specific memory/effector CD4+ T cell frequencies by flow cytometry: evidence for a novel, antigen-specific homeostatic mechanism in HIV-associated immunodeficiency

The highly regulated secretion of effector cytokines by CD4+ T cells plays a critical role in immune protection against pathogens such as cytomegalovirus. Here, we directly compare the frequency and functional characteristics of cytomegalovirus-specific CD4+ memory/effector T cells in normal and HIV+ subjects using a novel, highly efficient multiparameter flow cytometric assay that detects the rapid intracellular accumulation of cytokine(s) after short-term (6 h) in vitro antigen stimulation. Responses in this assay correlate precisely with independent measures of sensitization history (e.g., seroreactivity), and allow the simultaneous assessment of multiple cytokines in single effector T cells. Healthy HIV- individuals manifested an average of 0.71, 0.72, 0.38, and 0.06% CD4+ T cells responding to cytomegalovirus with gamma-IFN, TNF-alpha, IL-2, and IL-4 production, respectively, with the simultaneous production of gamma-IFN, TNF-alpha, and IL-2 being the most common effector phenotype. Significantly, overall cytomegalovirus-specific CD4+ effector frequencies were markedly higher among 40% of HIV+ subjects (2.7-8.0%), and demonstrated a predominately polarized gamma-IFN+/TNF-alpha+/IL-2-/IL-4- phenotype. In contrast, CD4+ effector frequencies for heterologous, nonubiquitous viruses such as the mumps virus were low or absent in the HIV+ group. These data suggest the existence of homeostatic mechanisms in HIV disease that selectively preserve memory T cell populations reactive with ubiquitous pathogens such as cytomegalovirus-likely at the expense of T cell memory to more sporadically encountered infectious agents.

Measurement of CD69 induction in the assessment of immune function in asymptomatic HIV-infected individuals

Peripheral blood mononuclear cells from many asymptomatic HIV-infected patients exhibit defects in cytokine production and impaired proliferative responses in vitro but the mechanisms underlying this subclinical immune deficiency are controversial. To determine whether abnormalities in the earliest events following receptor engagement may help to explain the in vitro immune dysfunction, we measured the inducibility of the early activation marker CD69 in T cells from asymptomatic HIV-infected individuals in response to stimulation with anti-CD2 or anti-CD3 mAb. In a whole blood assay, we found that induction of CD69 was markedly impaired in CD4+ T cells from later-stage HIV-infected patients (CD4 counts 200-400/mm3) compared to uninfected controls. Among early stage patients (CD4 > 400/mm3), a subset (29%) had impaired CD69 induction. CD69 responses were equally depressed after stimulation through the CD3 or CD2 receptor pathways. Survey of a panel of immunophenotypic markers and propensity for apoptosis demonstrated a significant association between depressed induction of CD69 and decreased percentages of CD4+CD26+ and CD4+CD95+ cells but no association with the level of apoptosis. These data indicate that defects in T lymphocyte activation through CD3 and CD2 can be measured within hours of receptor stimulation in asymptomatic HIV-infected individuals and might be useful to monitor as an indicator of immune function in these patients.

Direct demonstration of cytokine synthesis heterogeneity among human memory/effector T cells by flow cytometry

The array of cytokines produced by T cells in effector sites is a primary means by which these cells mediate host defense. It is well recognized that cloned T cells are heterogeneous with regard to cytokine synthesis and, thus, in their ability to mediate specific immune responses, but the extent to which the patterns of cytokine secretion observed in cloned cells reflect actual populations of memory/effector T cells existing in vivo is largely unknown. Here, we report our findings using a multiparameter flow cytometric assay that allows simultaneous determination of an individual T-cell's ability to produce multiple cytokines and its phenotype after only short (4 to 8 hours) in vitro incubation with an activating stimulus and the secretion inhibitor Brefeldin A. This assay shows a rapid accumulation of interleukin-2 (IL-2), IL-4, and gamma-interferon (gamma-IFN) in the cytoplasm of CD4+ cells after stimulation with either accessory cell-independent (phorbol 12-myristate 13-acetate [PMA] + ionomycin [I]) or accessory cell-dependent (staphylococcal enterotoxins [SE] A and B) T-cell-activating stimuli. Further analysis showed that production of gamma-IFN and IL-4 is predominantly, if not exclusively, restricted to the CD45ROhigh memory/effector T-cell subset, whereas IL-2 may be produced by both the CD45ROhigh and CD45ROlow subsets. Simultaneous determination of IL-2 and gamma-IFN production among CD45ROhigh/CD4+ T cells showed distinct subsets that produce each of these cytokines alone (an average of 30% for IL-2 alone, 8% for gamma-IFN alone), both (16%), or neither (46%). Similar analyses with the small IL-4-producing memory/effector T-cell subset (only 4.3% of total CD4+/CD45ROhigh T cells) showed that an average of 51% of these IL-4-producing cells also synthesize average of 51% of these IL-4-producing cells also synthesize IL-2, 23% synthesize only IL-4, 16% synthesize all three cytokines, and 9.6% synthesize IL-4 and gamma-IFN. These patterns of cytokine synthesis were found to be similar with both PMA + I and SEA/SEB stimulation and were observed in both peripheral blood memory/effector CD4+ T cells and in T cells of similar phenotype obtained from cutaneous delayed-type hypersensitivity sites. Taken together, these data strongly support the in vivo existence of human memory/effector T-cell subsets with "preprogrammed" cytokine synthesis potential, although they suggest that these subsets may be more complex than originally proposed in the TH1/TH2 hypothesis.

Rapid flow cytometric method for measuring lymphocyte subset activation

Standard in vitro methods for assessing T-cell activation have typically measured either the proliferative responses of peripheral blood mononuclear cell (PBMC) cultures to various provocative stimuli employing tritiated thymidine incorporation or the secretion of specific cytokines from activated cells. These bulk assay methods suffer the drawback of being lengthy assays, and, in addition, they do not provide information about functional responses of individual lymphocyte subsets. This report describes a three-color flow cytometric method for the rapid analysis (4 hours) of individual T-cell subsets in whole blood responding to various provocative stimuli, including pokeweed mitogen, the comitogenic monoclonal antibodies (mAbs) CD2/CD2R, the superantigen staphylococcal enterotoxin B (SEB), and the specific antigen Candida albicans. After 4 hours, CD69 expression in response to CD2/CD2R paralleled thymidine incorporation measured after 72 hours. Variations in the proportions of CD4+ and CD4- T cells expressing CD69 were observed with different stimuli. These observations demonstrate the potential of multiparameter flow cytometry for the investigation of functional responses of individual T-cell subsets to a variety of stimuli in whole blood.

Structural characterization of a cross-reactive idiotype shared by monoclonal antibodies specific for the human CD4 molecule

A panel of mouse monoclonal anti-CD4 antibodies was characterized in terms of idiotypic expression by using specific anti-idiotypic antibody (anti-Id) reagents generated in rabbits immunized with anti-Leu3a, a monoclonal anti-CD4 which inhibits the human immunodeficiency virus (HIV) gp120 binding to CD4. Direct binding and competitive inhibition assays demonstrate that the majority of monoclonal anti-CD4 antibodies able to recognize CD4 epitopes overlapping the epitope recognized by anti-Leu3a expressed an antigen-combining site-related cross-reactive idiotype (IdX). Western blot analysis was used to demonstrate that this IdX is associated primarily with the light (L) chain of the monoclonal anti-CD4 antibodies. To further characterize the structural basis of the IdX, the nucleotide sequence of the variable region of the L kappa chain of anti-Leu3a was determined. Peptides corresponding to the first, second, and third complementarity determining regions (CDRs) of the L chain of anti-Leu3a were synthesized and used to immunize rabbits. All anti-peptide antisera recognized the immunizing peptide, the cognate anti-Leu3a molecule, and several other monoclonal anti-CD4 antibodies by direct binding assays. Western blot analysis utilizing the anti-CDR peptide reagents demonstrates that the reactivity to the monoclonal anti-CD4 antibodies was L chain-specific. The anti-Id generated by immunizing with the intact anti-Leu3a molecule failed to recognize the three L chain-derived CDR synthetic peptides, suggesting that the IdX requires the presence of the three-dimensional configuration of the L chain for its expression. The broad range of reactivity exhibited by the antipeptide antisera indicates that the majority of mouse monoclonal anti-CD4 antibodies characterized in this study utilize L chains encoded by a single germ line variable (V) region kappa (V kappa) chain gene or by V kappa genes that belong to the same gene family.

Epitopes of human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins recognized by antibodies in the sera of HIV-1-infected individuals

Sera from human immunodeficiency virus (HIV)-infected study subjects and controls were analyzed by enzyme-linked immunosorbent assay using 10 synthetic peptides to identify epitopes of HIV envelope glycoproteins (ENVgp) that were recognized by antibodies. Two epitopes of HIV ENVgp, ENVP466 (amino acids 466-481) and ENVP497 (amino acids 497-509), were recognized by antibodies in the sera of most HIV-infected individuals. The frequency of individuals with detectable serum antibodies to these two epitopes was not associated with the stage of HIV disease. Purified antibodies to ENV497 had only very weak neutralizing activity against infectious HIV. These data suggest that a particular dominant type of antibody response to HIV's ENVgp has minimal protective effects. These and other studies to identify and stimulate immune responses to selected epitopes of HIV antigens may be useful in the design of vaccines to prevent or treat HIV infections.

Anti-idiotypic antibodies of a predefined specificity generated against CDR3VH synthetic peptides define a private anti-CD4 idiotype

A synthetic peptide corresponding to the third complementarity determining region (CDR) of the heavy chain (CDR3VH) of anti-Leu3a, a monoclonal anti-CD4 antibody which inhibits HIV gp120 binding to CD4, was used to elicit specific anti-peptide antibodies in rabbits. The anti-peptide antisera showed anti-idiotypic antibody (anti-Id) activity and recognized both the immunizing peptide and the intact cognate protein by ELISA. In addition, the antisera reacted with isolated heavy chains of anti-Leu3a by Western blot analysis. The lack of reactivity with a panel of monoclonal anti-CD4 antibodies suggested that the anti-peptide antisera recognize a private idiotype (Id) associated with the anti-Leu3a CDR3VH region. Further studies demonstrated the inability of the rabbit antisera to inhibit the binding of anti-Leu3a to the CD4 molecule. In addition, soluble recombinant CD4 was unable to inhibit the binding of the rabbit anti-peptide antisera to anti-Leu3a indicating that the CDR3VH region may not be involved in CD4 recognition. Anti-Id containing sera from mice, rabbits and nonhuman primates immunized with the intact anti-Leu3a molecule did not bind the CDR3VH synthetic peptide, suggesting that the corresponding region of anti-Leu3a may not represent an immunodominant idiotypic determinant in thes e species. These results suggest the potential use of synthetic peptides corresponding to immunoglobulin variable (V) region amino acid sequences in generating anti-Id reagents of a predefined specificity. In addition, V-region synthetic peptides may be useful in mapping the idiotopes recognized by an anti-Id response to the cognate molecule.

Activated T cells and monocytes have characteristic patterns of class II antigen expression

The expression of human histocompatibility class II Ag was measured on activated T cells and monocytes by quantitative mAb binding in direct two-color immunofluorescence. Monocytes activated by IFN-gamma bound an average of 2 x 10(6) DR-specific mAb, 3 x 10(5) DQ-specific mAb, and 7 x 10(5) DP-specific mAb per cell. For T cells activated by anti-CD3, a subpopulation bound 1 x 10(5) DR-specific mAb, 5 x 10(4) DQ-specific mAb and 5 x 10(4) DP-specific mAb per cell. These measurements were obtained after establishing a base line of class II Ag expression on resting B cells and monocytes. Resting B cells and those monocytes that were positive for class II Ag bound identical amounts of mAb; 3 x 10(4) DR-specific mAb, 3 x 10(3) DQ-specific mAb and 2 x 10(4) DP-specific mAb. However, most resting monocytes (75%) expressed only DR Ag. In the process of studying the expression of class II Ag on T cells, it was necessary to define and analyze the activated T cell state. Cell cultures activated with 0.3 ng/ml anti-CD3 had the highest expression of class II Ag on T cells, whereas those activated with 3.0 ng/ml anti-CD3 had the highest expression of IL-2R on T cells. Addition of IL-2 had no further effect on DR Ag expression on T cells but did up-regulate IL-2R expression. Reducing the initial monocyte concentration before activating T cells increased class II Ag expression on T cells without affecting IL-2R expression. The results obtained on T cell activation suggest that perhaps a lymphokine may be made by CD3-activated T cells which induces class II Ag expression on T cells.

Activated T cells and monocytes have characteristic patterns of class II antigen expression

The expression of human histocompatibility class II Ag was measured on activated T cells and monocytes by quantitative mAb binding in direct two-color immunofluorescence. Monocytes activated by IFN-gamma bound an average of 2 x 10(6) DR-specific mAb, 3 x 10(5) DQ-specific mAb, and 7 x 10(5) DP-specific mAb per cell. For T cells activated by anti-CD3, a subpopulation bound 1 x 10(5) DR-specific mAb, 5 x 10(4) DQ-specific mAb and 5 x 10(4) DP-specific mAb per cell. These measurements were obtained after establishing a base line of class II Ag expression on resting B cells and monocytes. Resting B cells and those monocytes that were positive for class II Ag bound identical amounts of mAb; 3 x 10(4) DR-specific mAb, 3 x 10(3) DQ-specific mAb and 2 x 10(4) DP-specific mAb. However, most resting monocytes (75%) expressed only DR Ag. In the process of studying the expression of class II Ag on T cells, it was necessary to define and analyze the activated T cell state. Cell cultures activated with 0.3 ng/ml anti-CD3 had the highest expression of class II Ag on T cells, whereas those activated with 3.0 ng/ml anti-CD3 had the highest expression of IL-2R on T cells. Addition of IL-2 had no further effect on DR Ag expression on T cells but did up-regulate IL-2R expression. Reducing the initial monocyte concentration before activating T cells increased class II Ag expression on T cells without affecting IL-2R expression. The results obtained on T cell activation suggest that perhaps a lymphokine may be made by CD3-activated T cells which induces class II Ag expression on T cells.

In vitro activation of T lymphocytes from human immunodeficiency virus (HIV)-seropositive blood donors. I. Soluble interleukin 2 receptor (IL2R) production parallels cellular IL2R expression and DNA synthesis

We investigated the relationship of soluble interleukin 2 receptor (sIL2R) production to cellular IL2R expression and DNA synthesis by mitogen-stimulated mononuclear cells from blood donors seropositive for human immunodeficiency virus (HIV). SIL2R was measured using an enzyme-linked immunosorbent assay which employed 2 anti-IL2R monoclonal antibodies recognizing distinct IL2R epitopes. Decreased phytohemagglutinin-induced DNA synthesis and cellular IL2R expression were accompanied by decreased levels of sIL2R in cell culture supernatants. Similar findings were observed for pokeweed mitogen-induced responses. There was no detectable spontaneous secretion of sIL2R into culture supernatants by unstimulated mononuclear cells from either HIV-seropositive or control seronegative donors. These findings indicate that the in vitro T-cell activation defects which characterize HIV infection include decreased sIL2R production, as well as decreased cellular IL2R expression and DNA synthesis. Further, they show that assessment of supernatant sIL2R levels can be used as a valid, reliable assay for T-cell activation.

Monoclonal antibodies, L-35 and L-36, define novel T cell activation antigens

Two novel T cell specific activation antigens were characterized and were defined by monoclonal antibodies developed against mitogen-stimulated human T cells. These antigens, designated as L-35 and L-36 were expressed on both the CD 4(Leu-3) and the CD 8(Leu-2) subsets of activated but not resting T cells. Moreover these antigens were not expressed on a number of T, B, and myeloid tumor cell lines. L-35 and L-36 were expressed on interleukin 2 (IL 2)-dependent cloned T cell lines, and were weakly expressed on the T cell tumor line, HSB-2. L-35 was expressed on granulocytes and a small subset of thymocytes. SDS-PAGE analysis of 125I-labeled lysates from phytohemagglutinin (PHA)-activated T cells demonstrated that L-35 existed as a complex of 32,000 and 97,000 dalton polypeptides under reducing and nonreducing conditions. Anti-L-36 immunoprecipitated a 90,000 dalton structure from PHA-activated cell lysates prepared with CHAPS detergent. When immunoprecipitates were analyzed from [35S]methionine labeled lysates, anti-L-35 precipitated only the 97,000 dalton component, suggesting that the 32,000 dalton subunit of L-35 complex was not synthesized by the activated cell population. Furthermore anti-L-35 did not immunoprecipitate a 32,000 dalton component from 125I-labeled lysates of anti-Leu-4 or Con A-activated cells, suggesting that the 32,000 dalton component of the L-35 complex may represent a subunit of PHA. The 32,000 dalton protein could not, however, be precipitated from cells incubated with PHA for less than 1 day. These results suggested that anti-L-35 recognizes a 97,000 dalton structure expressed on activated T cells, and that upon activation by PHA, becomes associated with a subunit of this mitogen.

Monoclonal antibodies, L-35 and L-36, define novel T cell activation antigens

Two novel T cell specific activation antigens were characterized and were defined by monoclonal antibodies developed against mitogen-stimulated human T cells. These antigens, designated as L-35 and L-36 were expressed on both the CD 4(Leu-3) and the CD 8(Leu-2) subsets of activated but not resting T cells. Moreover these antigens were not expressed on a number of T, B, and myeloid tumor cell lines. L-35 and L-36 were expressed on interleukin 2 (IL 2)-dependent cloned T cell lines, and were weakly expressed on the T cell tumor line, HSB-2. L-35 was expressed on granulocytes and a small subset of thymocytes. SDS-PAGE analysis of 125I-labeled lysates from phytohemagglutinin (PHA)-activated T cells demonstrated that L-35 existed as a complex of 32,000 and 97,000 dalton polypeptides under reducing and nonreducing conditions. Anti-L-36 immunoprecipitated a 90,000 dalton structure from PHA-activated cell lysates prepared with CHAPS detergent. When immunoprecipitates were analyzed from [35S]methionine labeled lysates, anti-L-35 precipitated only the 97,000 dalton component, suggesting that the 32,000 dalton subunit of L-35 complex was not synthesized by the activated cell population. Furthermore anti-L-35 did not immunoprecipitate a 32,000 dalton component from 125I-labeled lysates of anti-Leu-4 or Con A-activated cells, suggesting that the 32,000 dalton component of the L-35 complex may represent a subunit of PHA. The 32,000 dalton protein could not, however, be precipitated from cells incubated with PHA for less than 1 day. These results suggested that anti-L-35 recognizes a 97,000 dalton structure expressed on activated T cells, and that upon activation by PHA, becomes associated with a subunit of this mitogen.

Induction of interleukin 2 from a murine B cell tumor by a factor found in immune serum

The murine B cell tumor line 2 PK-3 secretes T cell growth factor activity after incubation for 6 to 48 hr with a factor present in heterologous immune serum. T cell growth factor derived from 2 PK-3 was compared with IL 2 produced by the Con A-induced T lymphoma cell line EL-4 G12. These studies indicated that T cell growth factor activities derived from both cell lines were similar with respect to m.w., pI values, and the ability to support growth of two IL 2-dependent T cell clones. Three preparations of immune sera were found to be active in the induction of IL 2 activity from 2 PK-3 cells, including rabbit anti-mouse brain, rabbit anti-complete Freund's adjuvant, and goat anti-mouse Ig. None of these preparations, however, induced IL 2 from EL-4 G12 cells. It was also observed that LPS synergized with immune serum to produce enhanced activity. Normal sera prepared from unimmunized animals were not active in the induction of IL 2 activity. Fractionation of immune serum on protein A Sepharose suggested that the IL 2-inducing agent is not IgG.

Induction of interleukin 2 from a murine B cell tumor by a factor found in immune serum

The murine B cell tumor line 2 PK-3 secretes T cell growth factor activity after incubation for 6 to 48 hr with a factor present in heterologous immune serum. T cell growth factor derived from 2 PK-3 was compared with IL 2 produced by the Con A-induced T lymphoma cell line EL-4 G12. These studies indicated that T cell growth factor activities derived from both cell lines were similar with respect to m.w., pI values, and the ability to support growth of two IL 2-dependent T cell clones. Three preparations of immune sera were found to be active in the induction of IL 2 activity from 2 PK-3 cells, including rabbit anti-mouse brain, rabbit anti-complete Freund's adjuvant, and goat anti-mouse Ig. None of these preparations, however, induced IL 2 from EL-4 G12 cells. It was also observed that LPS synergized with immune serum to produce enhanced activity. Normal sera prepared from unimmunized animals were not active in the induction of IL 2 activity. Fractionation of immune serum on protein A Sepharose suggested that the IL 2-inducing agent is not IgG.

Mechanisms controlling TCGF production by cloned sublines of EL-4 azgr in response to stimulation by anti-Thy-1 antibody

The effect of xenogeneic anti-Thy-1 antibody on T cell growth factor (TCGF) production by T lymphoma cell lines has been examined as a model system for T cell activation. EL-4 G12 (a cloned subline of the producer EL-4 azgr cell line) produced TCGF when stimulated by a high concentration of anti-Thy-1, but none was induced by low concentrations of anti-Thy-1. Large amounts of TCGF were produced when these cells were cultured with Fc-receptor positive (FcR+) accessory cells. TCGF production by EL-4 G12 showed dose response kinetics similar to TCGF production by anti-Thy-1-stimulated, purified normal spleen T cells. Goat anti-rabbit IgG (GaRIG) and protein A substituted for this accessory helper effect, but neither FcR+ cells nor Protein A worked when (Fab')2 anti-Thy-1 was used instead of IgG anti-Thy-1. Anti-T-200 monoclonal antibody inhibited anti-Thy-1-induced TCGF production by EL-4 G12 and accessory cells. Phorbol myristic acetate and lymphocyte-activating factor also substituted in part for the accessory cell help. The data suggest there are at least 2 different accessory cell help mechanisms in anti-Thy-1-induced TCGF production, anti-Thy-1-bound membrane aggregation either by GaRIG, Protein A or FcR, and a LAF-dependent mechanism.

Mechanisms controlling TCGF production by cloned sublines of EL-4 azgr in response to stimulation by anti-Thy-1 antibody

The effect of xenogeneic anti-Thy-1 antibody on T cell growth factor (TCGF) production by T lymphoma cell lines has been examined as a model system for T cell activation. EL-4 G12 (a cloned subline of the producer EL-4 azgr cell line) produced TCGF when stimulated by a high concentration of anti-Thy-1, but none was induced by low concentrations of anti-Thy-1. Large amounts of TCGF were produced when these cells were cultured with Fc-receptor positive (FcR+) accessory cells. TCGF production by EL-4 G12 showed dose response kinetics similar to TCGF production by anti-Thy-1-stimulated, purified normal spleen T cells. Goat anti-rabbit IgG (GaRIG) and protein A substituted for this accessory helper effect, but neither FcR+ cells nor Protein A worked when (Fab')2 anti-Thy-1 was used instead of IgG anti-Thy-1. Anti-T-200 monoclonal antibody inhibited anti-Thy-1-induced TCGF production by EL-4 G12 and accessory cells. Phorbol myristic acetate and lymphocyte-activating factor also substituted in part for the accessory cell help. The data suggest there are at least 2 different accessory cell help mechanisms in anti-Thy-1-induced TCGF production, anti-Thy-1-bound membrane aggregation either by GaRIG, Protein A or FcR, and a LAF-dependent mechanism.

Anti-Thy-1-mediated T cell activation. Role of soluble factors and expression of interleukin 2 receptors on T cells

Rabbit anti-Thy-1 antibody bound to T cells induces the appearance of T cell growth factor (interleukin 2, IL2) receptors and the production of IL2. IL2 receptors induction by this means occurs within a short time span, and independent of any demonstrable accessory cell. A source of exogenous or endogenous IL2 is apparently the only requirement for proliferation after these receptors are expressed. IL2 production, on the other hand, is accessory cell-dependent, and this help is mediated via Fc receptors on the accessory cell. IL2 production in this model is demonstrable at 4-6 h, or earlier, and is proliferation-independent. X-irradiation actually augments apparent IL2 production. The data are consistent with the hypothesis that a differentiated subset of T cells in any mixed population is responsible for IL2 production.

Mitogen activation of human chronic lymphatic leukemia cells. I. Synthesis and secretion of immunoglobulin

The response of CLL (chronic lymphatic leukemia) lymphocytes to PHA, PWM, and Con A with respect to changes in surface markers and synthesis and secretion of immunoglobulin were examined. After PHA stimulation the percentage of cells bearing readily detectable surface immunoglobulin (SmIg) diminished rapidly whereas cells forming rosettes with sheep erythrocytes (E-rosettes) increased from less than 1% to 30 to 50%. The great majority of blast-transformed cells were E-rosette-positive cells with a small population of SmIg-positive blast cells also observed. Ig production in four of seven CLL lymphocyte populations was increased 2.5 to greater than 40-fold after 4 to 6 days of culture in the presence of PHA. In contrast, pokeweed mitogen did not affect Ig synthesis. Furthermore, the Ig secreted into the culture supernatant fluids from seven of eight CLL cases examined consisted almost entirely of free light chain molecules. In contrast, the cell lysates contained a significant proportion of intact Ig molecules. These results indicate that CLL cells can, under certain circumstances, be stimulated to synthesize and secrete increased amounts of Ig, but that there is a basic defect in the biosynthetic mechanism of these cells which result in the secretion of free light chains rather than intact immunoglobulin molecules.

Bacteriophage resistance in Bacillus subtilis 168, W23, and interstrain transformants

Strains of Bacillus subtilis 168 deficient in glucosylated teichoic acid vary in their resistance to bacteriophage infection. Although glucosylated teichoic acid is important for bacteriophage attachment, the results demonstrate that alternate receptor sites exist. Non-glucosylated cell wall mutants could be assigned to specific classes (gtaA, gtaB, gtaC) by their pattern of resistance to three closely related bacteriophages (phi25, phie, SP82). In addition to glucosylation, the type of teichoic acid was also important for bacteriophage attachment. B. subtilis strains 168 and W23 have different teichoic acids in their cell walls and have varied susceptibilities to bacteriophage infection. Transfer of bacteriophage resistance from strain W23 into a derivative of strain 168 was accomplished. The resistant bacteria obtained were imparied in their ability to adsorb bacteriophage and in their capacity to be transfected by bacteriophage deoxyribonucleic acid.

Recognition at cell surfaces: phytohaemagglutinin-lymphocyte interaction

Many aspects of cell behaviour are regulated by the interaction of extracellular ligands with specific receptors exposed on the cell surface. The receptors correspond to membrane proteins and expecially glycoproteins. A key event in regulation is the transmission across the surface membrane of the information resulting from receptor-ligand interaction. The activation of lymphocytes by Phaseolus vulgaris phytohaemagglutinin (PHA) provides a convenient experimental model for the study of the molecular basis of receptor-ligand interaction and the molecular consequences of interaction. The receptor mediating lymphocyte activation by PHA is probably a unique glycoprotein which is present to the extent of about 3 X 10(4) molecules/cell. The PHA-receptor complex solubilized in 1% sodium deoxycholate has a molecular size of about 3 X 10(5). The primary event in the activation process is probably an increase in the permeability of the surface membrane to Ca2+. This may be achieved by PHA cross-linking ('patching') the receptors to form a polar channel that permits an influx of Ca2+.

Relationship between enhanced turnover of phosphatidylinositol and lymphocyte activation by mitogens

1. Various lectins [phaseolus vulgaris phytohaemagglutinin, Glycine max (soy-bean) agglutinin, Triticum vulgaris (wheat-germ) agglutinin and Axinella polyploides agglutinin] and antibodies to pig Ig (immunoglobulin) that are found by pig lymphocytes were assessed in terms of their capacities to stimulate lymphocyte transformation and to enhance phosphatidylinositol turnover. Transformation was measured after 45h of culture by incorporation of [6-(3)H]thymidine into DNA, whereas phosphatidylinositol metabolism was assessed after 1h of cultuis and G. max agglutinins and rabbit antibodies to pig Ig) increased phosphatidylinositol turnover, but non-transforming agents (T. vulgaris and A. polyploides agglutinins and Fab fragments of rabbit antibodies to pig Ig) failed to induce any significant enhancement. Subsequent cross-linkage of the bound, non-transforming Fab fragments with a goat antiserum to rabbit Ig stimulated transformation and phosphatidylinositol turnover. 3. Each transforming agent gave characteristic optimal dose responses that were similar for both phosphatidylinositol turnover and transformation. 4. The results indicate that activation of T- and B-lymphocytes is accompanied by enhanced phosphatidylinositol turnover and that in the case of B-cells this enhancement depends on the cross-linkage of surface receptors. They are consistent with the proposal that turnover represents an essential early step in the transformation process.