OX40 promotes Bcl-xL and Bcl-2 expression and is essential for long-term survival of CD4 T cells

It is important to understand which molecules are essential for long-lived immunity. We show that OX40 (CD134) is required with CD28 for the survival of CD4 T cells following antigen-driven expansion. In contrast to CD28-/- T cells, which show defects early, OX40-/- T cells are relatively unimpaired in IL-2 production, cell division, and expansion. However, OX40-/- T cells fail to maintain high levels of Bcl-xL and Bcl-2 4-8 days after activation, and undergo apoptosis. Conversely, OX40 stimulation promotes Bcl-xL and Bcl-2 and suppresses apoptosis. Moreover, retroviral transduction of OX40-/- T cells with Bcl-xL or Bcl-2 reverses their survival defect. Thus, a temporal relationship exists between CD28 and OX40, with OX40 being a critical regulator of antigen-driven T cell survival.

CD28, Ox-40, LFA-1, and CD4 modulation of Th1/Th2 differentiation is directly dependent on the dose of antigen

The involvement of specific accessory/costimulatory molecules in differentiation to Th1 and Th2 phenotypes is controversial. Reports suggest that molecules such as CD4, CD28, and Ox-40 support Th2 differentiation and suppress Th1 differentiation, whereas others such as LFA-1 support Th1 responses and suppress Th2 responses. We have previously defined an in vitro model of differentiation that is absolutely dependent on the initial dose and affinity of peptide presented to a naive CD4 cell. The dose and affinity of Ag regulate autocrine production of IL-2, IL-4, and IFN-gamma, which in turn govern differentiation to Th1 and Th2 phenotypes. We have used this system to confirm that CD4, CD28, and Ox-40 interactions can promote, and LFA-1 interactions can suppress, differentiation of cells secreting the Th2 cytokines IL-5 and IL-13. However, for CD4 and LFA-1, this is only seen over a certain range of peptide doses. In addition, CD28 and Ox-40 interactions also promote Th1 differentiation. In general, agonist Abs to accessory molecules shifted the response curves for IFN-gamma, IL-5, and IL-13 to lower doses, whereas antagonist reagents resulted in similar curves shifted toward the higher doses. We conclude that ligation of cell surface accessory receptors enables low doses of Ag to promote responses normally induced only by higher doses. Individual receptors do not intrinsically regulate one cytokine phenotype or another, suggesting that differentiation is controlled by the level of expression of multiple accessory molecule pairs integrated with the number and affinity of peptide/MHC complexes.

Qualitative changes accompany memory T cell generation: faster, more effective responses at lower doses of antigen

The generation of memory T cells is critically important for rapid clearance and neutralization of pathogens encountered previously by the immune system. We have studied the kinetics of response and Ag dose requirements for proliferation and cytokine secretion of CD4+ memory T cells to examine whether there are qualitative changes which might lead to improved immunity. TCR Tg CD4+ T cells were primed in vitro and transferred into T cell-deficient hosts. After 6 or more weeks, the persisting T cells were exclusively small resting cells with a memory phenotype: CD44high CD62L+/- CD25-. Memory CD4 T cells showed a similar pattern of response as naive cells to peptide analogues with similar Ag dose requirements for IL-2 secretion. However, memory cells (derived from both Th2 and Th1 effectors) displayed faster kinetics of cytokine secretion, cell division, and proliferation, enhanced proliferation in response to low doses of Ag or peptide analogues, and production of IL-4, IL-5, and IFN-gamma. These results suggest there is a much more efficient response of CD4 memory T cells to Ag re-exposure and that the expanded functional capacity of memory cells will promote a rapid development of effector functions, providing more rapid and effective immunity.

Switch recombination in a transfected plasmid occurs preferentially in a B cell line that undergoes switch recombination of its chromosomal Ig heavy chain genes

Ab class switching is induced upon B cell activation in vivo by immunization or infection or in vitro by treatment with mitogens, e. g. LPS, and results in the expression of different heavy chain constant region (CH) genes without a change in the Ab variable region. This DNA recombination event allows Abs to alter their biological activity while maintaining their antigenic specificity. Little is known about the molecular mechanism of switch recombination. To attempt to develop an assay for enzymes, DNA binding proteins, and DNA sequences that mediate switch recombination, we have constructed a plasmid DNA substrate that will undergo switch recombination upon stable transfection into the surface IgM+ B cell line (I.29 mu), a cell line capable of undergoing switch recombination of its endogenous genes. We demonstrate that recombination occurs between the two switch regions of the plasmid, as assayed by PCRs across the integrated plasmid switch regions, followed by Southern blot hybridization. Nucleotide sequence analysis of the PCR products confirmed the occurrence of S mu-S alpha recombination in the plasmid. Recombination of the plasmid in I.29 mu cells does not require treatment with inducers of switch recombination, suggesting that recombinase activity is constitutive in I.29 mu cells. Recombination does not require high levels of transcription across the switch regions of the plasmid. Fewer recombination events are detected in four different B and T cell lines that do not undergo switch recombination of their endogenous genes.

Peptide dose, affinity, and time of differentiation can contribute to the Th1/Th2 cytokine balance

Opposing viewpoints exist regarding how Ag dose and affinity modulate Th1/Th2 differentiation, with data suggesting that both high and low level stimulation favors Th2 responses. With transgenic T cells bearing a single TCR, we present novel data, using peptides differing in affinity for the TCR, that show that the time period of differentiation can determine whether Th1 or Th2 responses predominate as the level of initial stimulation is altered. Over the short term, IFN-gamma-producing cells were induced by lower levels of stimulation than IL-4-producing cells, although optimal induction of both was seen with the same high level of stimulation. Over the long term, however, high doses of high affinity peptides led selectively to IFN-gamma-secreting cells, whereas IL-4- and IL-5-secreting cells predominated with lower levels of initial signaling, brought about by moderate doses of high affinity peptides. In contrast, too low a level of stimulation at the naive T cell stage, with low affinity peptides at any concentration, promoted only IL-2-secreting effectors or was not sufficient for long term T cell survival. These results demonstrate that the level of signaling achieved through the TCR is intimately associated with the induction of distinct cytokine-secreting T cells. We show that dose, affinity, time over which differentiation occurs, and initial production of IL-4 and IFN-gamma all can contribute to which T cell subset will predominate. Furthermore, these data reconcile the two opposing views on the effects of dose and affinity and provide a unifying model of Th1/Th2 differentiation based on strength of signaling and length of response.

High antigen density and IL-2 are required for generation of CD4 effectors secreting Th1 rather than Th0 cytokines

We reevaluated the effects of Ag dose on the polarization of CD4 effectors generated in vitro from naive pigeon cytochrome c-specific TCR transgenic T cells under conditions in which we could eliminate contaminating non-naive CD4 cells and the effects of heterogeneous Ag-presenting populations. When the possibility of contaminating non-naive T cells was reduced by using T cells from transgenic mice on a RAG-2(-/-) background, Ag dose did not have a significant effect in Th1 and Th2 polarization unless exogenous IL-2 was initially added to cultures. Effectors generated were uniformly Th0 but produced only IL-2 in substantial amounts. When exogenous IL-2 was added to priming cultures, T cells secreting a Th0 phenotype (large quantities of IL-2, IL-4, IL-5, and IFN-gamma) developed, except at very high doses of Ag, where there was a striking reduction in IL-4 and IL-5 secretion. Our results imply that Ag dose does not have a direct effect on Th1/Th2 polarization, except under conditions that include a high level of TCR ligation and in the presence of high levels of IL-2, where production of Th2 cytokines may be down-regulated by a mechanism that is not yet clear.

Modulation of naive CD4 T cell activation with altered peptide ligands: the nature of the peptide and presentation in the context of costimulation are critical for a sustained response

Altered peptide ligands containing single amino acid substitutions have the potential to be used for modulating immune function. Using a panel of moth cytochrome c peptides, we demonstrate that different phases of naive CD4 T cell response are alternately modulated depending on altered peptide ligand dose and accessory molecule expression by APC. Weak agonists presented at high concentration, and with costimulation, efficiently induced early phase naive T cell activation as assessed by IL-2R/CD69 expression, but could only promote sufficient IL-2 for a short-lived proliferative response. In contrast, strong agonists and heteroclitic peptides induced early phase T cell activation even at low concentrations with costimulation, and allowed sustained IL-2 secretion and proliferation. In the absence of accessory molecule help, early and late phase activation was impaired with weak agonists, whereas strong agonists partially compensated for a lack of costimulation for early phase activation, and also promoted enhanced IL-2 with sustained proliferation. These studies support the hypothesis that the naive T cell response will be determined by the balance between provision of accessory molecule help and the affinity of peptide/MHC complexes for individual TCRs, and suggest that extended IL-2 production is the main facet of naive CD4 activation that is affected by altering the nature of the peptide.

B lymphocyte development and activation independent of MHC class II expression

A murine model of MHC class II deficiency created by targeted gene disruption was used to investigate whether class II expression influences B cell maturation and function. There appeared to be fewer total B cell precursors, a higher proportion of which were in a very early stage of maturation, in class II-deficient vs control bone marrow; however, the differences did not reach statistical significance. Mature B cells were unaffected; IgM, IgD, B220, and CD5 surface expression were similar in class II-deficient and control animals. Serum Ig determinations revealed that the class II-deficient animals had elevated IgM but decreased IgG1 (and, variably, IgE) compared to control. The antibody response against thymic-independent Ag was intact in class II-animals, as was the in vitro response of small resting B cells from class II deficient animals to stimulation with polyclonal B cell activators. Preactivated T cells were able to induce differentiation and proliferation of class II-deficient, small resting B cells. Together, these data indicate that B cell development, T cell-independent, and T cell-dependent B-cell activation, can occur independently of class II MHC expression.

B lymphocyte development and activation independent of MHC class II expression

A murine model of MHC class II deficiency created by targeted gene disruption was used to investigate whether class II expression influences B cell maturation and function. There appeared to be fewer total B cell precursors, a higher proportion of which were in a very early stage of maturation, in class II-deficient vs control bone marrow; however, the differences did not reach statistical significance. Mature B cells were unaffected; IgM, IgD, B220, and CD5 surface expression were similar in class II-deficient and control animals. Serum Ig determinations revealed that the class II-deficient animals had elevated IgM but decreased IgG1 (and, variably, IgE) compared to control. The antibody response against thymic-independent Ag was intact in class II-animals, as was the in vitro response of small resting B cells from class II deficient animals to stimulation with polyclonal B cell activators. Preactivated T cells were able to induce differentiation and proliferation of class II-deficient, small resting B cells. Together, these data indicate that B cell development, T cell-independent, and T cell-dependent B-cell activation, can occur independently of class II MHC expression.

CD45 alternative exon expression in murine and human CD4+ T cell subsets

Leukocytes express a family of high m.w. glycoproteins called leukocyte common Ag (CD45), which are involved in phosphotyrosine signal transduction. Antibodies to different CD45 isoforms distinguish functionally different CD4+ T cell subsets in humans, rats, and mice. Selected protein isoforms are expressed through a process of exon splicing that is cell-type and differentiation-state specific. Splicing of the three variable exons, A, B, and C, which encode amino acids located near the extracellular amino terminus of the protein, potentially results in generation of eight different mRNA transcripts. The purpose of the present study was to determine the relative levels of all eight different CD45 transcripts present in a panel of murine CD4+ T cell lines and normal murine and human CD4+ T cell subsets separated with antibodies to CD45 variable exons. We show, as expected, that the broad features of CD45 surface isoform expression in these cells can be accounted for by the relative amounts of the eight differentially spliced transcripts. Unexpectedly, all the differences in CD45 isoform expression among the CD4+ T cell subpopulations that we measured could be accounted for by differences in the overall level of variable exon expression. We did not see differences among T cell populations in the relative expression of particular variable exons. Exon B was always found in greater abundance than exons C or A. Of the dual exon species, only AB and BC were found in CD4+ T cells. The AC species was undetectable. Human CD4+ T cells, especially those in the naive subset, express higher levels of CD45 variable exons than murine CD4+ T cells.

CD45 alternative exon expression in murine and human CD4+ T cell subsets

Leukocytes express a family of high m.w. glycoproteins called leukocyte common Ag (CD45), which are involved in phosphotyrosine signal transduction. Antibodies to different CD45 isoforms distinguish functionally different CD4+ T cell subsets in humans, rats, and mice. Selected protein isoforms are expressed through a process of exon splicing that is cell-type and differentiation-state specific. Splicing of the three variable exons, A, B, and C, which encode amino acids located near the extracellular amino terminus of the protein, potentially results in generation of eight different mRNA transcripts. The purpose of the present study was to determine the relative levels of all eight different CD45 transcripts present in a panel of murine CD4+ T cell lines and normal murine and human CD4+ T cell subsets separated with antibodies to CD45 variable exons. We show, as expected, that the broad features of CD45 surface isoform expression in these cells can be accounted for by the relative amounts of the eight differentially spliced transcripts. Unexpectedly, all the differences in CD45 isoform expression among the CD4+ T cell subpopulations that we measured could be accounted for by differences in the overall level of variable exon expression. We did not see differences among T cell populations in the relative expression of particular variable exons. Exon B was always found in greater abundance than exons C or A. Of the dual exon species, only AB and BC were found in CD4+ T cells. The AC species was undetectable. Human CD4+ T cells, especially those in the naive subset, express higher levels of CD45 variable exons than murine CD4+ T cells.

Comparison of motility stimulants for cryopreserved human semen

Caffeine, pentoxifylline, 2-deoxyadenosine, cyclic adenosine monophosphate (cAMP), relaxin, adenosine, kallikrein, and calcium were compared for their ability to stimulate motility of cryopreserved sperm. Caffeine, pentoxifylline, and 2-deoxyadenosine significantly increased the percentage of motile sperm at 15, 30, 45, and 60 minutes after administration. Sperm velocity was significantly increased by caffeine at 0, 15, 30, and 45 minutes, and by pentoxifylline at 0, 45, and 60 minutes. Consistent stimulation was not observed for other chemicals. Caffeine, pentoxifylline, and 2-deoxyadenosine were then examined for their ability to provide motility stimulation after removal with washing. With the exception of caffeine, percent motility and velocity for stimulated and untreated sperm were similar after washing. A significant reduction in motility was observed at 48 hours after washing for caffeine. The percentage of hamster oocytes penetrated at 24 hours after washing was significantly reduced for caffeine, 2-deoxyadenosine, and pentoxifylline combined with 2-deoxyadenosine. Pentoxifylline-treated sperm showed no reduction in fertilizing capacity. These results indicate that, of the chemicals examined, pentoxifylline is superior for motility stimulation of cryopreserved sperm.