Stimulation of murine T cell subsets with anti-CD3 antibody. Age-related defects in the expression of early activation molecules

Splenocytes from young (3 to 4 mo) and aged (24 to 26 mo) C57BL/6 mice were stimulated with anti-CD3 epsilon mAb in vitro. At the time of peak DNA synthesis (day 2), cells from aged mice incorporated congruent to 60% less [3H]TdR than cells from young mice. This age-related defect was not attributable to gross differences in anti-CD3 does optima, response kinetics, accessory cell function, numbers of T cells cultured, CD4+:CD8+ cell ratios or surface levels of CD3 epsilon molecules. In an attempt to analyze pre-S phase events in these responses, we monitored CD4+ and CD8+ cells in splenocyte cultures for the time-dependent expression of three T cell activation markers: RL388 Ag and IL-2R and transferrin R. Parallel analyses of mean T cell size and cell cycle phase distributions were performed. Non-activated T cells from both age groups similarly expressed moderate levels of RL388 Ag, low levels of transferrin R, and undetectable levels of IL-2R. Analysis of stimulated T cells revealed, in both age groups: 1) detectable increases in expression of all three markers by 6 h of culture, and continued increases associated with blastogenesis and G1 phase transit and 2) a preferential stimulation of the CD8+ subset to a state of high level marker expression. Age group comparisons of activation marker expression over time suggested that the age-related defect reflects proportionally smaller fractions of CD4+ and CD8+ cells that respond normally, rather than a general defect in all T cells or a subset-specific defect. Finally, we found that supernatants from aged donor cell cultures stimulated with anti-CD3 contained less Il-2 than those of young controls. Addition of an IL-2 containing supernatant to aged donor cell cultures increased, but did not restore, the S phase response on day 2; however, the response on day 3 was comparable to the peak (day 2) response of young controls. These data suggest that exogenous IL-2 can improve the aged response, perhaps by expanding the fraction of normally reactive T cells.     

Age-related dysregulation in CD8 T cell homeostasis: kinetics of a diversity loss

Relative diversity and representation of peripheral T cells bearing different TCR Vbeta families are remarkably tightly regulated between birth and advanced adulthood. By contrast, individual elderly humans and C3H.SW and B10.BR aged mice display drastic disruption in such regulation. It was suggested that the alterations in the murine aged T cell compartment were due to age-related clonal T cell expansions (TCE). Here, we studied the kinetics of homeostatic dysregulation of T cell populations in aged C57BL/6 (B6) mice. Using mAb staining, we show that the percentages of alphabeta+CD8+ or CD4+ T cells bearing different TCRVbeta elements remain virtually constant in mice up to 12 mo of age. In 22-mo-old mice, however, there is a dramatic disturbance of this pattern owing to the emergence of CD8+ TCE. Expanded T cells did not show any obvious bias in Vbeta usage and were derived in all cases examined thus far from a single clone. TCE appeared later in life, compared with B cell clonal expansions. However, and in contrast to those detected in humans, TCE were frequently unstable disappearing within 2-4 mo, with other TCE appearing within the same time frame. Additional studies carried on thymic T cells, thymectomized mice, and young T transferred cells into Rag1-/- mice suggest that the clonal expansions occur in the periphery and that their onset is accelerated by decreased thymic output and/or function(s).     

Clonal anergy is maintained independently of T cell proliferation

Ag encounter in the absence of proliferation results in the establishment of T cell unresponsiveness, also known as T cell clonal anergy. Anergic T cells fail to proliferate upon restimulation because of the inability to produce IL-2 and to properly regulate the G(1) cell cycle checkpoint. Because optimal TCR and CD28 engagement can elicit IL-2-independent cell cycle progression, we investigated whether CD3/CD28-mediated activation of anergic T cells could overcome G(1) cell cycle block, drive T cell proliferation, and thus reverse clonal anergy. We show here that although antigenic stimulation fails to elicit G(1)-to-S transition, anti-CD3/CD28 mAbs allow proper cell cycle progression and proliferation of anergic T cells. However, CD3/CD28-mediated cell division does not restore Ag responsiveness. Our data instead indicate that reversal of clonal anergy specifically requires an IL-2-dependent, rapamycin-sensitive signal, which is delivered independently of cell proliferation. Thus, by tracing proliferation and Ag responsiveness of individual cells, we show that whereas both TCR/CD28 and IL-2-generated signals can drive T cell proliferation, only IL-2/IL-2R interaction regulates Ag responsiveness, indicating that proliferation and clonal anergy can be independently regulated.     

Differences in the expression profiles of CD45RB, Pgp-1, and 3G11 membrane antigens and in the patterns of lymphokine secretion by splenic CD4+ T cells from young and aged mice

Previous studies indicate that the 3G11, CD45RB, and Pgp-1 determinants are differentially expressed on CD4+ T cell subsets in the mouse. We used multicolor immunofluorescence staining and flow cytofluorometric analysis to examine the expression of each of these determinants on splenic CD4+ cells from young (age 3 to 6 mo) and aged (age 24 to 26 mo) C57BL/6 mice. The CD4+ pool from aged mice contained significantly reduced numbers of 3G11+ and CD45RBhi cells, but increased numbers of Pgp-1hi cells, in comparison with the young group. Analysis of the simultaneous expression of all three subset determinants on CD4+ cells revealed that, in young mice, the major fraction (greater than 50%) was 3G11+CD45RBhiPgp-1lo. Among the less prevalent cell phenotypes, reductions in 3G11 expression correlated with decreases in CD45RB levels and increases in Pgp-1 levels. The phenotype that dominated the young group (3G11+CD45RBhiPgp-1lo) was approximately fivefold less represented in the aged group. The CD4+ pool from aged mice was characterized by increases in the 3G11-CD45RBvariablePgp-1hi and the 3G11+CD45RBloPgp-1hi phenotypes. To evaluate possible age-associated differences in cytokine secretion patterns by splenic CD4+ cells, purified CD4+ cells from each age group were stimulated in vitro with immobilized anti-CD3 epsilon mAb and accessory cells. At various times thereafter, supernatants from cultures were tested for IL-2 and IL-4 content by using the CTLL.6 and 11.6 bioassays, respectively, and the CD4+ cells were assayed for [3H]TdR uptake. Cell cultures from the aged group exhibited similar peak IL-2 accumulation and lower peak [3H]TdR uptake, but greatly increased peak IL-4 accumulation, as compared with cell cultures from the young group. The expression patterns of subset determinants, in conjunction with cytokine secretion profiles, indicate that, in aged mice, marked alterations occur in the subset composition of the splenic CD4+ cell pool. These findings are discussed in the context of previous findings on changes in T cell reactivity with advancing donor age.     

Impaired antigen-induced CD8+ T cell clonal expansion in aging is due to defects in antigen presenting cell function

CD8+ T cell activation depends on interaction with antigen-presenting cells (APCs) and this interaction leads to the expansion of T cells with the capacity to control infection. Using professional APCs, we demonstrate that with age, the duration of APC-T cell contact time required to achieve clonal expansion increases. Na?ve CD8+ T cells from aged mice showed no defect in antigen-induced proliferation when stimulated with APC from young mice. In contrast, CD8+ T cells from young mice exhibited reduced clonal expansion and secreted significantly lower amounts of IFN-gamma when stimulated by APCs from aged mice. The aged APCs were defective in costimulatory molecule expression and cytokine and chemokine secretion. These data indicate that defects in APC function lead to poor T cell clonal expansion and function in aging.     

CD25-expressing CD8+ T cells are potent memory cells in old age

We have recently described an IL-2/IL-4-producing CD8+CD25+ non-regulatory memory T cell population that occurs in a subgroup of healthy elderly persons who characteristically still have a good humoral response after vaccination. The present study addresses this specific T cell subset and investigates its origin, clonal composition, Ag specificity, and replicative history. We demonstrate that CD8+CD25+ memory T cells frequently exhibit a CD4+CD8+ double-positive phenotype. The expression of the CD8 alphabeta molecule and the occurrence of signal-joint TCR rearrangement excision circles suggest a thymic origin of these cells. They also have longer telomeres than their CD8+CD25- memory counterparts, thus indicating a shorter replicative history. CD8+CD25+ memory T cells display a polyclonal TCR repertoire and respond to IL-2 as well as to a panel of different Ags, whereas the CD8+CD25- memory T cell population has a more restricted TCR diversity, responds to fewer Ags, and does not proliferate in response to stimulation with IL-2. Molecular tracking of specific clones with clonotypic primers reveals that the same clones occur in CD8+CD25+ and CD8+CD25- memory T cell populations, demonstrating a lineage relationship between CD25+ and CD25- memory CD8+ T cells. Our results suggest that CD25-expressing memory T cells represent an early stage in the differentiation of CD8+ cells. Accumulation of these cells in elderly persons appears to be a prerequisite of intact immune responsiveness in the absence of naive T cells in old age.     

Interleukin 2 receptor expression by T cells in human aging

Aged individuals have depressed cell-mediated immunity and diminished T cell proliferation to mitogenic and antigenic stimuli. Because T cell responses depend on the surface expression and normal function of interleukin 2 receptors, we measured the quantities and affinities of cell surface IL-2R and the amount of soluble IL-2R alpha chain (p55) release in vitro in PHA-stimulated mononuclear cells from healthy aged (greater than or equal to 65 years old) and young (less than or equal to 39 years old) donors. At the peak of the PHA response, the fraction of cells expressing IL-2R alpha chain (CD25+) was lower in the aged (43% vs 56%, P = 0.033). Relative to the lower proliferation and CD25 expression, old donor cells released unexpectedly high quantities of soluble alpha chain into culture supernatants. However, the average affinities and the mean numbers of high- and low-affinity surface receptors per CD25+ cell were equivalent in cells from eight pairs of aged and young donors (1850 vs 1586 high affinity, and 20,655 vs 23,466 low affinity, P greater than 0.2 for both). The soluble IL-2R released by stimulated cells had no effect on proliferative responses, because addition of saturating doses of exogenous recombinant IL-2 did not increase cellular proliferation, and addition of soluble anchor-minus recombinant IL-2R alpha chain did not suppress it. These results indicate that in healthy older individuals, diminished numbers of T cells can be induced to express cell surface IL-2R following mitogenic stimulation, although aged CD25+ can express a normal complement of IL-2R molecules. In the aged, either CD25+ cells release excessive quantities or a subset of cells synthesizes and releases soluble IL-2R alpha chain into the extracellular environment without expressing it on the cell surface.     

Differential in vitro activation of CD8-CD4+ and CD4-CD8+ T lymphocytes by combinations of anti-CD2 and anti-CD3 antibodies

Purified peripheral blood T lymphocytes and the CD8-CD4+ and CD4-CD8+ T cell subsets, exhaustively depleted of APC have been studied for their capacity to respond to mAb directed against the CD3-Ti Ag-specific TCR complex and against the CD2 SRBCR. It is demonstrated that high affinity IL-2R can be readily induced by either anti-CD3 and/or anti-CD2 stimulation. However, IL-2 production can be observed only in the CD4+CD8- T cell subset. These results clearly contrast data obtained with purified CD4-CD8+ T cells, which are able to proliferate when the CD3-Ti complex is activated in the presence of APC. The data presented in the present study demonstrate that a simplified model for T cell activation and clonal expansion of the two major T cell subsets involve only the CD3-Ti complex and the CD2 Ag. Under conditions where the activation signals for the T cells are restricted only to the activation of CD3-Ti and CD2, the CD4+CD8- T cells respond with IL-2 production and expression of high affinity IL-2R, whereas the CD4-CD8+ T cell subset depends on exogenous IL-2 provided by the CD4+CD8- cells. These data do not, however, exclude an involvement of other cell-surface signals for regulation and control of T cell activation and T cell effector functions.     

Immune responses against allogeneic and syngeneic tumors in aged C57BL/6 mice

Aged C57BL/6 (B6) mice could reject allogeneic BALB/c RL male 1 tumor as efficiently as young B6 mice. However, in vitro analysis showed impaired generation of cytotoxic T cell response in aged B6 mice against allogeneic tumor. The reaction could be augmented by the addition of recombinant interleukin-2 (rIL-2). Enzyme-linked immunospots (ELISPOT) produced by CD8+ T cells purified from spleen cells showed no reduction in aged mice. The findings suggested that the number of CD8+ T cells capable of reacting against allogeneic H-2 antigens was similar in young and aged B6 mice. Low cytotoxic T lymphocyte (CTL) responsiveness in aged B6 mice appeared to have resulted from low responsiveness of CD4+ T cells producing IL-2. Although CTL generation was apparently impaired, strong multiple antigenicity of allogeneic tumor evoked a rejection response in aged B6 mice. On the other hand, no rejection response was observed against syngeneic EL4 tumor in aged B6 mice even after depletion of CD4+ CD25+ immunoregulatory cells. Depletion of CD4+ CD25+ cells caused rejection of EL4 tumor in young B6 mice. The findings suggested that aged B6 mice were incapable of inducing effector cells against weak tumor antigens. Only marginal CTL response and small number of ELISPOTs were generated in young but not aged B6 mice against EL4. Addition of rIL-2 to the culture augmented EL4 killing and ELISPOTs in spleen cells from young and aged B6 mice.     

Impaired clonal expansion in athymic nude CD8+CD4- T cells

A comparative study of the phenotype and immune functions of highly purified CD8+CD4- T cells obtained from the spleen and thymus of normal mice and from the spleen of athymic nude mice was conducted. Of seven individual normal and nude mice examined, the range of V beta 8+ cells among CD8+ T cells was a heterogeneous 4.3 to 30.5% for athymic nude mice and a much more uniform spread from 14.7 to 18.5% for normal mice. In six of the seven nude mice examined, the fraction of V beta 8+ cells was below the lower limit of the V beta 8 distribution in normal mice. However, one of the seven nude mice contained nearly twice the percentage of normal V beta 8+ cells. A reduction in the density of V beta 8 as well as CD3 Ag expression was also observed in athymic CD8+CD4- cells although an Ly-6-linked Ag, B4B2 displayed a highly increased expression. Considering the battery of Ag analyzed in entirety, athymic CD8+CD4- T cells were clearly distinct from their "counterpart" CD8+CD4- T cells isolated from either thymus or spleen of normal (euthymic) mice. Anti-CD3-mediated triggering of the TCR:CD3 complex caused extensive clonal proliferation in cultures to which single responding CD8+ T cells had been deposited. Under identical conditions, however, anti-CD3 caused little, if any clonal expansion in CD8+ cells from athymic nude mice. Highly purified athymic CD8+CD4- cells produced readily detectable IL-2R expression and IL-2 synthesis and secretion upon stimulation by anti-CD3 and by Con A. Production of IL-2 by purified athymic CD8+CD4- cells was due to CD8+CD4- cells and not due to a minor population of contaminating CD8- cells as anti-CD8 + C treatment completely abrogated the ability of athymic CD8+CD4- cells to produce IL-2. Despite IL-2 production and IL-2R expression by athymic nude CD8+CD4- T cells in response to anti-CD3 and to Con A, an impaired proliferative response followed.     

CD4+CD25- T cells in aged mice are hyporesponsive and exhibit suppressive activity

Studies on humans and rodents have established that functional deterioration of CD4 T cells occurs with aging. We report in this study that approximately 70% of CD4(+)CD25(-) T cell preparations from individual 24-mo-old mice are hyporesponsive to in vitro stimulation with anti-CD3 Ab. The remaining 30% of CD4(+)CD25(-) T cell preparations showing the intermediate or normal responsiveness in the primary stimulation also exhibit the hyporesponsive properties after primary stimulation. Both of these hyporesponsive aged CD4(+)CD25(-) T cells could inhibit the proliferation of cocultured CD4(+)CD25(-) T cells from young mice, like CD4(+)CD25(+) T cells, which have recently been demonstrated as an immune regulator in young mice. Another experiment revealed that hyporesponsive aged CD4(+)CD25(-) T cells arrest the cell division of cocultured young CD4(+)CD25(-) T cells. The suppressive activity observed in aged CD4(+)CD25(-) T cells is aging-dependent, not mediated by humoral factors, cell-contact dependent, and broken by the addition of IL-2 or anti-GITR Ab, but not by anti-CTLA-4 Ab. These studies show that aging not only leads to a decline in the ability to mount CD4(+)CD25(-) T cell responses, but at the same time, also renders these aged CD4(+)CD25(-) T cells suppressive.     

Identification of the B cell derived T cell colony promoting activity to soluble CD23.

We previously reported that supernatants of phytohemagglutinin (PHA)-stimulated normal human B cells (NBCsup) contain a T cell colony promoting activity. NBCsup were able to (a) increase the number of secondary colonies generated under PHA and interleukin-2 (IL-2) stimulation by peripheral blood-derived primary T colony cells, (b) enhance the ability of CD4+ but not CD8+ peripheral blood T cells to form agar colonies in the presence of PHA and IL-2 and (c) support in vitro differentiation of CD2-3-4-8- prothymocytes into CD2+3+4+ T cells. This activity was therefore refered to as Prothymocyte Differentiating Activity (PTDA). Subsequent studies pointed to striking biochemical and cell source homologies between this B cell derived factor and the 25-kDa soluble CD23 (sCD23). sCD23 has been recently found to display prothymocyte differentiating activity.     

Vitamin E, signalosomes and gene expression in T cells

CD4+T cells from aged humans or mice show significant reductions in IL-2 production upon activation. The resulting decreased proliferation is linked to higher risks of infection in the elderly. Several lines of evidence indicate that intrinsic defects preferentially affecting the naïve subset of CD4+T cells contribute to this reduced IL-2 production. Comparison of the biochemical pathways that transduce activation signals from the T cell receptor to the IL-2 promoter in young and old CD4+T cells has demonstrated age-related impairments at initial molecular events, in particular the phosphorylation of kinases and adapter proteins involved in the formation of signalosomes - complex multiprotein assemblies that provide the framework for effective signal transduction. Confocal microscopy has demonstrated a series of age-related impairments in effective immune synapse formation. Vitamin E can reverse many of these CD4+T cell age-associated defects, including reduced levels of phosphorylation of critical signaling/adapter proteins as well as defective immune synapse formation. Vitamin E also enhances IL-2 production, expression of several cell cycle control proteins, and proliferation. Although the precise mechanisms underlying this effect are not understood, it is possible that this antioxidant lipophilic vitamin can prevent the propagation of polyunsaturated fatty acid peroxidation in the cell membrane, influence the biochemical characteristics of specific lipid bilayer microdomains involved in signal transduction, modulate the activity of kinases/phosphatases, or interact with intracellular receptors.     

Age-associated decline in responses of na?ve T cells to in vitro immunization reflects shift in glucocorticoid sensitivity.

Na?ve T lymphocytes from young mice can be immunized to protein antigens in vitro if the initial exposure to antigen is followed by a brief period of clonal expansion in the presence of both the glucocorticoid dexamethasone (at 10(-8) M) and antibodies to Interleukin-10 (IL-10). These cultures produce cell lines that respond to antigen rechallenge by proliferation and cytokine secretion. T cells from older mice, however, do not respond under these conditions unless the dexamethasone concentration is raised to levels (10(-7) M) that are inhibitory for T cells of young mice. Suitably timed exposure to dexamethasone can also increase proliferative responses to polyclonal activation via the CD3 component of the T cell receptor, and again optimal responses are obtained from old mice only at steroid concentrations that are super-optimal for young T cells. Diminished sensitivity to glucocorticoid effects may contribute to the poor responses of aged mice to novel immunogens.     

Characterization of T cell clones from an athymic mouse.

Although Thy-1+ lymphocytes have been observed in lymphoid tissues of athymic mice, attempts to analyze these cells on the clonal level have previously yielded only populations of CD4-CD8+ cytolytic T cells. Furthermore, studies of responses of these cells to various mitogenic stimuli have demonstrated significant defects in the ability of these cells to proliferate in culture. We report here on the cloning and maintenance in long term culture of T cells from an athymic mouse stimulated in vitro with allogeneic spleen cells. Of 10 Thy-1+ clones, 7 CD4+CD8- and 3 CD4-CD8+ Ag-specific cells were obtained. Among the CD4+ T cells, we observed a variety of specificities, including an autoreactive I-Aq specific clone, a minor lymphocyte stimulating determinant (Mls)-reactive clone, and five allo-I-Ad-specific CD4+ clones; a class II-specific CD4-CD8+ clone was also obtained. In addition, we observed two Thy-1-CD3+ clones (one of which is also CD4+ and expresses V beta 8) which are constitutively responsive to the lymphokines IL-2 and IL-4. Of 11 clones tested, 7 produce IL-2 and/or IL-4 lymphokines after stimulation through the TCR, whereas 4 do not, requiring exogenous lymphokines for optimal responses to Ag. Of 10 clones tested for IL-2R expression, 3 had notably low levels, correlating with low proliferative responses to IL-2. The results reveal the spectrum of T cells available to a mouse which is congenitally athymic and describe the heterogeneity of immune defects expressed in such cells at the clonal level.     

T cell effector function and anergy avoidance are quantitatively linked to cell division

We have shown previously that T cells activated by optimal TCR and CD28 ligation exhibit marked proliferative heterogeneity, and approximately 40% of these activated cells fail entirely to participate in clonal expansion. To address how prior cell division influences the subsequent function of primary T cells at the single cell level, primary CD4+ T cells were subjected to polyclonal stimulation, sorted based on the number of cell divisions they had undergone, and restimulated by ligation of TCR/CD28. We find that individual CD4+ T cells exhibit distinct secondary response patterns that depend upon their prior division history, such that cells that undergo more rounds of division show incrementally greater IL-2 production and proliferation in response to restimulation. CD4+ T cells that fail to divide after activation exist in a profoundly hyporesponsive state that is refractory to both TCR/CD28-mediated and IL-2R-mediated proliferative signals. We find that this anergic state is associated with defects in both TCR-coupled activation of the p42/44 mitogen-activated protein kinase (extracellular signal-related kinase 1/2) and IL-2-mediated down-regulation of the cell cycle inhibitor p27kip1. However, these defects are selective, as TCR-mediated intracellular calcium flux and IL-2R-coupled STAT5 activation remain intact in these cells. Therefore, the process of cell division or cell cycle progression plays an integral role in anergy avoidance in primary T cells, and may represent a driving force in the formation of the effector/memory T cell pool.     

The effect of aging on the frequency,phenotype and cytokine production of human blood CD4 + CXCR5 + T follicular helper cells: comparison of aged and young subjects

Background

T cell-dependent B-cell responses decline with age, indicating declined cognate helper activity of aged CD4?+?T cells for B cells. However, the mechanisms remain unclear. T follicular helper (Tfh) cells, a novel T helper subset, play an essential role in helping B cells differentiation into long-lived plasma cells in germinal center (GC) or short-lived plasma cells. In the present study, we proposed that there might existe changes of proportion, phenotype or cytokine production of blood Tfh cells in healthy elderly individuals compared with healthy young individuals.

Results

The results showed that frequencies of aged blood CXCR5?+?CD4?+?Tfh cells increased compared with young subjects. Both aged and young blood CXCR5?+?CD4?+?Tfh cells constitutively expressed CD45RO, CCR7 and CD28, and few of these cells expressed CD69 or HLA-DR, which indicated that they were resting memory cells. There was no significant difference of IL-21 frequency production by aged blood CXCR5?+?CD4?+?Tfh determined by FACS compared with young individuals, however, aged PBMCs produced significantly higher levels of IL-21 evaluated by ELISA. Furthermore, there were no significant differences of percentages of IFN-γ, IL-4, IL-17 or IL-22 production by aged Tfh cells compared with their counterparts of young individuals respectively. However, frequencies of IL-17+ cells within aged CD4?+?CXCR5-T cells were markedly lower than in the young individuals. Furthermore we observed different frequencies of IFN-γ, IL-17, IL-4 or IL-22 production by Tfh or by CD4?+?CXCR5- cells in aged and young subjects respectively.

Conclusions

Our data demonstrated that the frequencies of blood memory CXCR5?+?CD4?+?Tfh cells increased in the elderly population. There were similar frequencies of Th characterized cytokine production such as IL-21, IFN-γ, IL-4, IL-17 or IL-22 in aged and young Tfh cells. However, aged PBMCs produced a significantly higher amount of IL-21 compare to young subjects.

     

CD1d-restricted NKT cells contribute to the age-associated decline of T cell immunity

NKT cells are known to regulate effector T cell immunity during tolerance, autoimmunity, and antitumor immunity. Whether age-related changes in NKT cell number or function occur remains unclear. Here, we investigated whether young vs aged (3 vs 22 mo old) mice had different numbers of CD1d-restricted NKT cells and whether activation of NKT cells by CD1d in vivo contributed to age-related suppression of T cell immunity. Flow cytometric analyses of spleen and LN cells revealed a 2- to 3-fold increase in the number of CD1d tetramer-positive NKT cells in aged mice. To determine whether NKT cells from aged mice differentially regulated T cell immunity, we first examined whether depletion of NK/NKT cells affected the proliferative capacity of splenic T cells. Compared with those from young mice, intact T cell preparations from aged mice had impaired proliferative responses whereas NK/NKT-depleted preparations did not. To examine the specific contribution of NKT cells to age-related T cell dysfunction, Ag-specific delayed-type hypersensitivity and T cell proliferation were examined in young vs aged mice given anti-CD1d mAb systemically. Compared with young mice, aged mice given control IgG exhibited impaired Ag-specific delayed-type hypersensitivity and T cell proliferation, which could be significantly prevented by systemic anti-CD1d mAb treatment. The age-related impairments in T cell immunity correlated with an increase in the production of the immunosuppressive cytokine IL-10 by splenocytes that was likewise prevented by anti-CD1d mAb treatment. Together, our results suggest that CD1d activation of NKT cells contributes to suppression of effector T cell immunity in aged mice.     

Athymic nude CD4+8- T cells produce IL-2 but fail to proliferate in response to mitogenic stimuli

A comparative study of immune functions of CD4+8- T cells isolated from normal and athymic nude mice by electronic cell sorting was performed. Athymic nude CD4+8- T cells expressed the TCR-associated CD3 molecule but the level of expression was significantly lower than that of normal CD4+8- T cells. Proliferative responses were studied upon stimulation by 1) the T cell mitogen Con A; 2) anti-CD3 mediated cross-linking of the CD3:TCR complex, and 3) the combined action of PMA + ionomycin. All three mitogenic stimuli caused readily detectable cell division in normal (euthymic) CD4+8- T cells. In marked contrast, none of the mitogenic stimuli induced significant proliferation in athymic nude CD4+8- T cells. The failure of athymic nude CD4+8- T cells to proliferate occurred over a wide range of mitogen concentrations and over a 4-day observation period. Neither exogenously supplied rIL-2 or mixed lymphocyte culture supernatant had any effect on the impaired proliferative response by athymic nude CD4+8- T cells. Although IL-2 was produced by athymic nude CD4+8- T cells at a reduced level when compared to normal CD4+8- T cells, it was nevertheless readily detected upon stimulation with either Con A or anti-CD3. Furthermore, stimulation of athymic nude CD4+8- T cells by anti-CD3 induced the expression of the p55 chain of IL-2R on the cell surface. Therefore, despite production of IL-2 and induced expression of IL-2R, athymic nude CD4+8- T cells failed to undergo cell division.     

Differences in allergen-induced T cell activation between allergic asthma and rhinitis: Role of CD28, ICOS and CTLA-4

Background

Th2 cell activation and T regulatory cell (Treg) deficiency are key features of allergy. This applies for asthma and rhinitis. However with a same atopic background, some patients will develop rhinitis and asthma, whereas others will display rhinitis only. Co-receptors are pivotal in determining the type of T cell activation, but their role in allergic asthma and rhinitis has not been explored. Our objective was to assess whether allergen-induced T cell activation differs from allergic rhinitis to allergic rhinitis with asthma, and explore the role of ICOS, CD28 and CTLA-4.

Methods

T cell co-receptor and cytokine expressions were assessed by flow cytometry in PBMC from 18 house dust mite (HDM) allergic rhinitics (R), 18 HDM allergic rhinitics and asthmatics (AR), 13 non allergic asthmatics (A) and 20 controls, with or without anti-co-receptors antibodies.

Results

In asthmatics (A+AR), a constitutive decrease of CTLA-4+ and of CD4+CD25+Foxp3+ cells was found, with an increase of IFN-γ+ cells. In allergic subjects (R + AR), allergen stimulation induced CD28 together with IL-4 and IL-13, and decreased the proportion of CTLA-4+, IL-10+ and CD4+CD25+Foxp3+ cells. Anti-ICOS and anti-CD28 antibodies blocked allergen-induced IL-4 and IL-13. IL-13 production also involved CTLA-4.

Conclusions

T cell activation differs between allergic rhinitis and asthma. In asthma, a constitutive, co-receptor independent, Th1 activation and Treg deficiency is found. In allergic rhinitis, an allergen-induced Treg cell deficiency is seen, as well as an ICOS-, CD28- and CTLA-4-dependent Th2 activation. Allergic asthmatics display both characteristics.