CD45 isoforms expression on CD4+ and CD8+ T cells throughout life, from newborns to centenarians: implications for T cell memory

Is immune senescence reversible?

Many genes have been shown to be involved in the decline in immune function of the elderly. However, normal numbers of myeloid and lymphoid colonies can be grown from elderly bone marrow under optimal conditions and some thymic function is preserved well into adult life. It may also be possible to reverse partially declining thymic function by IL-7 treatment. Peripheral B and T cells show evidence of dysregulation with production of large clones, changes in subset distribution and altered signalling and cytokine production, particularly decreased IL-2 production in the mouse. The identification of these defects may lead to relatively simple procedures to improve vaccination for the elderly.

Age-related structural modulation of T lymphocyte-associated CD45 isoforms

A monoclonal antibody, specific to all conventional CD45 isoforms, was employed in two-dimensional (2D) sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting to investigate possible age-related differential expression of these isoforms among immature and mature thymocytes as well as CD4+ and CD8+ T cell subpopulations in the periphery of newly-born, young and aged BALB/c mice. In young mice, and to a lesser degree in newly-born mice, intra-thymic maturation seemed to be paralleled by the capacity of thymocytes to synthesize distinct CD45 isoforms constituted by extensively heterogeneous acidic charge entities. Thymocyte maturation in aged mice, on the other hand, was characterized by minimal heterogeneity, as the observed pattern was essentially similar to the immature population in 2D blots. As inferred from comparisons of 2D blots of sialylated and desialylated forms of the CD45 complex, age-related differences in isoforms expressed by the CD4+ and the CD8+ T cell subpopulations in the periphery resided mainly in the degree of sialylation of the constituent isoforms. Given the potential of the differential sialylation state of CD45 in altering the recognition properties of lymphocytes, regulation of CD45 sialylation with age may add another level of complexity to the lymphocyte surface phenotype, which in turn may be implicated in cell-cell interaction mechanisms during lymphocyte maturation and senescence.

Immunologic and virologic responses to HAART in severely immunocompromised HIV-1-infected children

OBJECTIVE

To determine the long-term immunologic and virologic effects of highly active antiretroviral therapy (HAART) in children with AIDS.

DESIGN

A prospective observational study.

SETTING

Two pediatric HIV clinics.

PARTICIPANTS

Twenty-five protease-inhibitor naive HIV-infected children (aged 2-18 years) with advanced disease (CD4 < or =6%).

INTERVENTION

HAART (one protease inhibitor and one or more nucleoside analogs). Diphtheria and tetanus immunization in six patients after 18 months of therapy.

MAIN OUTCOME MEASURES

Changes in percentage of CD4 cells and plasma HIV-1 RNA levels; post-treatment assays of lymphoproliferative responses to recall antigens; CD4 cell memory phenotype.

RESULTS

Median duration of follow-up was 18.8 months (range, 7.5-28 months). At baseline the CD4 cell percentage was 2% (range, 0-6%), this increased significantly to 16% (range, 3-48%) above baseline at 12 months (P = 0.002). The mean maximum CD4 cell increase was 20.7% (range 4-48%) which corresponds to 657x10(6) cells/l (range, 30-2240x10(6) cells/l) above baseline. By contrast, the median viral load was not significantly lower at 12 months than at baseline (P = 0.34), and only 25% of the patients had sustained undetectable viral load. Of the reconstituted CD4 cells 70% were naive, and none of the subjects had lymphoproliferative responses to tetanus and diphtheria although 40% did develop responses to Candida, an environmental antigen. A single immunization with diphtheria and tetanus toxoid produced lymphoproliferative responses to tetanus in three out of six patients.

CONCLUSIONS

HAART was associated with sustained increases in CD4 cell counts, despite a high incidence of 'virologic failure'. CD4 counts and the proportion of naive cells were higher than have been reported in adults, which may be a reflection of greater thymic activity in children. Memory cell clones for antigens encountered in the past which are not prevalent before therapy could not be expanded without additional antigenic exposure.

The immune system in the elderly: II. Specific cellular immunity

Numerous changes occur in the immune system with advancing age, probably contributing to the decreased immunoresponsiveness in the elderly. These changes are often associated with important clinical manifestations such as increased susceptibility to infection and cancer frequently observed in the elderly population. Although both cellular and humoral immune responses are modified with advancing age, much of the decrease in immunoresponsiveness seen in elderly populations is associated with changes in T cell responses. The loss of effective immune activity is largely due to alterations within the T cell compartment which occur, in part, as a result of thymic involution. Substantial changes in both the functional and phenotypic profiles of T cells have been reported with advancing age. In fact, two prominent features of immunosenescence are altered T cell phenotype and reduced T cell response. One of the most consistent changes noted in T cells with advancing age is the decrease in the proportion of naive T cells with a concomitant increase in T cells with an activated/memory phenotype. In addition, there is evidence that the T cell population from aged individuals is hyporesponsive. The observed functional changes include decreased responsiveness to T cell receptor stimulation, impaired T cell proliferative capacity, a decline in the frequency of CD4+ T cells producing IL-2 and a decreased expression in IL-2 receptors. These latter findings probably explain the loss of proliferative capability of T cells from aged individuals. There is also evidence of a decrease in the early events of signal transduction, decreased activation-induced intracellular phosphorylation, and decreased cellular proliferative response to T cell receptor stimulation. The present review analyzes the main changes of the T cell compartment characterizing immunosenescence and discusses the possible mechanisms underlying these disregulations and their clinical implications.

Further characterization of memory T cells existing in a case of CD8 deficiency

CD8 deficiency is a rare primary immunodeficiency caused by a defect of ZAP-70, which plays a pivotal role in T cell activation. We previously reported the existence of memory phenotype-CD4+ T cells in a case of CD8 deficiency, which demonstrates that activation signals through ZAP-70 are not essential to the phenotypic conversion of T cells from "naive" to "memory." In this study, we further characterized CD45RO+ T cells in a CD8 deficient patient. We showed that the patient's CD45RO+ T cell population had a wide variety of T cell receptor Vbeta-chain gene usage, and contained few clonally expanded T cells, while many clonally expanded T cells were present in the memory T cell population of age-matched healthy children. These results suggest that various kinds of antigens were involved in the differentiation of the patient's T cells, and that the differentiation into memory T cells was not accompanied by profound T cell proliferation. Moreover, our findings confirmed that the patient's CD45RO+CD4+ T cells had acquired effector-cytokine producing ability, indicating that there exists an alternative activation pathway which is independent of ZAP-70 for the acquisition of effector-cytokine producing ability.

Immunological changes in the elderly

Immunosenescence is a complex remodelling of the immune system which may contribute significantly to morbidity and mortality in the elderly. Much evidence suggests an association between immune function and longevity. It was advanced that individuals who have survived in good health to the maximum life span are equipped with optimal cell defense mechanisms. Despite the great number of studies on the immune system in the elderly, little is known of the biological basis of immunosenescence in humans. This is partly due to the contrasting results often obtained by the various investigators. One source of discrepancy is that diseases are frequent in aging, and the alterations observed in the immune parameters of the elderly could be a cause or alternatively a consequence of the underlying pathological processes. Undoubtedly some diseases to which aged people are particularly susceptible, such as infectious, autoimmune and neoplastic pathologies, include dysregulation of several immune functions in their pathogenesis. On the other hand, recent studies in healthy centenarians suggest that the immunological changes observed during aging are consistent with a reshaping, rather than a generalized deterioration, of the main immune functions. Considering that the number of old people is dramatically increasing, and that geriatric pathology is becoming an important aspect of clinical practice, it seems particularly interesting to review the peculiar findings in the immune system of the elderly so as to better understand their susceptibility to certain diseases, and the links between health and longevity.

Age-related defects in Th1 and Th2 cytokine production by human T cells can be dissociated from altered frequencies of CD45RA+ and CD45RO+ T cell subsets

The present study investigated whether age-related changes in the production of Th1 and Th2 cytokines by human T cells might be linked to altered frequencies of naive (CD45RA+) and memory (CD45RO+) T cell subsets. T cells from healthy elderly humans (n = 32) stimulated with anti-CD3epsilon monoclonal antibody OKT3 plus PMA produced significantly lower levels of IL-2 and IFNgamma (Th1 type) and of IL-4 (Th2 type) cytokines compared with T cells from young subjects. Although considerable heterogeneity was observed in the levels of cytokines produced by activated T cells from elderly individuals, linear regression analysis failed to demonstrate any significant shift in Th1 to Th2 type cytokine profiles of human T cells during aging. Sufficient T cells were available from eighteen elderly subjects to quantitate the levels of cytokine production in parallel with flow cytometry analysis of the frequencies of CD45RA+ naive and CD45RO+ memory T cells. Compared with the group of young subjects, the elderly group exhibited significant decreases in the frequencies of naive T cells with reciprocal increases in memory T cells. However, defects in Th1 and Th2 cytokine production were not significantly correlated with altered frequencies of naive/memory T cells among elderly individuals. In addition, those elderly individuals with normal frequencies of naive/memory T cells exhibited decreases in cytokine production comparable to the reductions observed for elderly donors with alterations in the frequencies of naive/memory T cells. These findings suggest that age-related defects in Th1 and Th2 cytokine production cannot be attributed entirely to alterations in the frequencies of naive/memory T cell subsets and point toward intrinsic aberrancies within human T cell cytokine networks during aging.

Age-related changes in the expression of CD95 (APO1/FAS) on blood lymphocytes

Aging is associated with alterations of the immune system, thought to be related to an increased susceptibility to infectious diseases, and possibly to cancer and autoimmunity in the elderly. In the present paper we report data obtained on freshly collected blood from 148 healthy subjects of different ages (from cord blood to 102 years old). The subjects were divided into seven age classes (cord blood, 3-11 years, 15-39 years, 41-60 years, 61-74 years, 75-84 years, 85-102 years) and their lymphocyte subsets and the expression of the apoptosis-related molecule CD95 were evaluated. In respect of lymphocyte subsets, the major differences were found in the cord-blood samples compared with the oldest old groups. In the cord-blood group, the absolute number of all the lymphocyte subsets was enhanced, but in the oldest group, an increase of CD16+ lymphocytes was observed, whereas CD19+ lymphocytes, which progressively decrease with age, continue to decrease further in the very old. The data show that the expression of CD95 increases until age 74 years, whereas in the oldest old it tends to decrease again. The trend of CD95 expression seems to be related to the change of expression of CD95 on CD4+ lymphocytes, because the CD8+/CD95+ population rose steadily throughout the entire age range. The evaluation of CD95+/CD45R0+ lymphocytes shows similar results to those observed analyzing CD95 on total lymphocytes. Furthermore, a constant increase of CD95+/CD28+ and a related decline of CD28+ lymphocytes was observed in all age groups. These data suggest that the expression of CD95 on the different subsets of lymphocytes can be considered a good marker for studies of immunosenescence, because it may be predictive of successful aging, and can partially explain the change in lymphocytes subsets in elderly.

Long-term immunologic effects of thymectomy in patients with myasthenia gravis

BACKGROUND

Thymectomy (Tx) is a common therapeutic option to treat myasthenia gravis (MG), but its effects on the immune system are still obscure in humans.

OBJECTIVE

We sought to evaluate long-term immunologic effects of therapeutic Tx in patients with MG.

METHODS

T- and B-cell subsets and T-cell repertoire were analyzed in 35 patients with MG, 16 with previous Tx (at least 8 years before), 6 with recent (<1 year) Tx, and 13 without Tx, as well as in 32 healthy subjects used as normal control subjects. Serum immunoglobulins and a variety of autoantibodies were also measured. A subsequent 3-year clinical follow-up was performed to verify the possible appearance of systemic autoimmune diseases.

RESULTS

The long-term thymectomized (Txd) patients had mild T-cell lymphopenia and an expansion of some Vbeta families among circulating CD4+ and CD8+ T cells. They displayed a normal number of total B and CD5+ B-circulating lymphocytes, but they also displayed a polyclonal increase in serum IgM and IgG associated with the presence of high levels of a variety of organ- and nonorgan-specific autoantibodies, including anti-dsDNA and anticardiolipin, without clinical evidence of autoimmune disease. These serologic abnormalities were not detectable in both non-Txd and recently Txd patients. After 3 years, 2 long-term Txd patients had systemic lupus erythematosus and an undifferentiated connective tissue disease.

CONCLUSIONS

The association between MG and laboratory findings of systemic autoimmune disease may be in part related to Tx rather than to MG. Tx may represent a risk for the development of systemic autoimmune disorders over years in patients with MG.

Postthymic Development of CD28−CD8+ T Cell Subset: Age-Associated Expansion and Shift from Memory to Naive Phenotype

During human aging, one of the major changes in the T cell repertoire is a dramatic expansion of T cells with the atypical CD28−CD8+ phenotype. In this study, we show that this increase is a consequence not only of an expansion in the CD28−CD8+ population but also of a decrease in the number of CD28+CD8+ T cells. The decrease in circulating CD28+CD8+ T cells is dramatically accelerated after the age of 50 and is not accompanied by an equivalent reduction in the CD28+CD4+ subset. Our findings confirm that aging leads to an accumulation of CD45RO+ T cells within the CD28+CD8+ subset as previously observed. Surprisingly, we found an increase in CD45RA+ expression with age in the CD28−CD8+ subset. Immune-phenotyping for activation markers, measurement of telomere DNA content, and cytokine production analysis indicate that the large majority of CD28−CD8+ T cells are Ag-experienced, despite their CD45RA+ phenotype. Our study further demonstrates that the poor proliferative response displayed by CD28−CD8+ T cells is not a consequence of telomere shortening. Also, analysis of cytokine production at the single cell level revealed that the proportions of IFN-γ+, IL-4+, and IL-10+ T cells are considerably higher among the CD28−CD8+ than the CD28+CD8+ subset. In summary, these data explain the presence of CD45RA+ T cells in the elderly, shed light on the phylogenetic origin of CD28−CD8+ T cells, and suggest a role for these cells in the immune senescence process.

Age-related changes in the absolute number of CD95 positive cells in T cell subsets in the blood

Comparison of the absolute number of cells in distinct T cells subsets expressing CD95 (Fas) was carried out in two populations of healthy female volunteers. In one population, the average age was 30 +/- 5 years, and in the second population the average age was 73 +/- 13 years. No significant difference was noted in the total number of lymphocytes, CD3+, CD4+, or CD8+ cells per microL of blood between the two age groups, but major differences were noted in the number of cells expressing CD95. A significant reduction was seen in the number of cells per microL of blood in both the CD4+ CD45RA+ CD95+ and CD8+ CD45RA+ CD95+ populations in the older group compared with the younger group. Within the memory pool significantly fewer CD8+ CD45RO+ CD95+ cells were found in the older population compared with the younger group. No such difference were found in the number of CD4+ CD45RO+ CD95+ cells between groups. Such a significant decline in the number of CD95+ cells, whose expression is known to be linked with activation, may be implicated as a mechanism by which cells that have reached a stage of replicative senescence remain in the peripheral T cell pool. Anti-CD3-mediated activation of cells from both groups revealed much lower proliferative responses from the older group, supporting the idea that there is an age-associated increase in the number of cells that have reached their replicative limit. These cells may not be lost from the peripheral pool because they fail to express CD95.

Environmental influence on age-related changes of human lymphocyte membrane viscosity using severe combined immunodeficiency mice as an in vivo model

Peripheral blood lymphocytes (PBL) of healthy elderly people show increased plasma membrane viscosity compared to young subjects, that inversely correlates with lymphocyte proliferation after mitogen stimulation in vitro. Maintenance of a constant membrane viscosity, which is necessary for proper cell function, is crucially dependent on the membrane lipid composition. The cellular lipid metabolism, and thus lymphocyte function, may be subject to modulation by diet or drugs. To study the susceptibility of membrane viscosity to environmental conditions, we established an in vivo model using severe combined immunodeficiency (SCID) mice: human peripheral blood lymphocytes from healthy young and old subjects were engrafted for three days intraperitoneally into SCID mice to offer identical environmental conditions. First, we demonstrate that human lymphocytes can take up and utilize murine lipoproteins: engrafted human PBL can participate in the mouse lipid metabolism, and an exchange of membrane lipids in vivo is, therefore, possible. Second, plasma membrane viscosity was determined before and after engraftment: before engraftment, PBL from the elderly showed a significantly higher membrane viscosity than that from young controls, but this difference vanished during engraftment into SCID mice, wherein cells from both age groups exhibited nearly identical values. It was, therefore, concluded that lymphocyte membrane viscosity is influenced by environmental factors, and that the age-related increase is, in principle, reversible.

Age-related loss of immunoregulatory function in peripheral blood CD8 T cells

CD8+ T cells from young individuals become inhibitory for the (Staphylococcus aureus + interleukin 2)-induced differentiation of autologous B cells into immunoglobulin secreting cells (ISC) after exposure to pokeweed mitogen (PWM), dimaprit or intracellular cAMP raising agents, such as forskolin or dibutyryl-cAMP. In the present study this immunoregulatory activity was found to be lacking in CD8+ T cells from peripheral blood lymphocytes (PBL) of aged (> 67 years old) subjects. Splenic CD8+ T cells from most individuals examined, including some aged subjects, exhibited this activity. While an age-related decrease in the CD8+ T cell subset, primarily in the virgin CD8+ T cells in PBL, was detected, this decrease was not sufficient to explain a total absence of activity. There was no age-related decrease in cAMP upregulation by forskolin or dimaprit in peripheral blood T cells. However, whereas PWM induced a highly significant increase in mRNA for transforming growth factor-beta (TGF-beta) in T cells from young individuals, no such increase could be detected in T cells from aged subjects. It is suggested that the decrease in immunoregulatory activity in PBL from the elderly may at least in part be due to a decrease in TGF-beta production.

Age-related changes in major lymphocyte subsets in cynomolgus monkeys

Age-related changes in major lymphocyte subsets were analyzed in 195 cynomolgus monkeys (Macaca fascicularis) aged from one month to 31 years. The percentages of CD20+ B cells in peripheral blood lymphocytes (PBL) decreased with age to five years of age, but after that, no significant change was observed. The percentages of CD16+ NK cells gradually increased during the first five years and reached the peak at from four to ten years of age, whereas the percentages of CD3+ T cells in PBL were relatively constant throughout the life. Among the T cells, the CD4+ CD8- T cells decreased, but CD4- CD8+ T cells increased within the first decade of life. We further analyzed the expressions of CD28 and CD29 molecules on T cells to determine the relation between age-related activation and phenotypic changes. Almost all CD4+ CD8- T cells (> 90%) were CD28+ at all ages analyzed, but a clear age-related decrease in CD28 expression was demonstrated in CD4- CD8+ T cells during the first ten years. In the case of CD29 expression, age-related increases in CD29hi cells were apparent in both CD4+ CD8- and CD4- CD8+ T cells during the first ten years. The percentages of CD29hi cells, however, were higher in CD4- CD8+ T cells than in CD4+ CD8- T cells in all ages analyzed. These results indicated that the age-related changes in percentages of major lymphocyte subsets as well as in phenotypes of T cells might be related to the maturation of the immune system including an increase in memory cells in cynomolgus monkeys.

T Cell Renewal Rates, Telomerase, and Telomere Length Shortening

Measurements on the average telomere lengths of normal human naive and memory T cells suggested that 1) naive and memory human T cells have similar division rates, and 2) that the difference between naive and memory cells reflects the degree of clonal expansion during normal immune reactions. Here we develop mathematic models describing how the population average of telomere length depends on the cell division rates of naive and memory T cells during clonal expansion and normal renewal. The results show that 1) telomeres shorten with twice the cell division rate, 2) that the conventional approach of estimating telomere length shortening per mean population doubling gives rise to estimates that are 39% larger than the “true” loss per cell division, 3) that naive and memory T cells are expected to shorten their telomeres at rates set by the division rate of the naive T cells only, i.e., irrespective of the division rate of memory T cells, 4) that the measured difference in the average telomere length between naive and memory T cells may largely reflect the difference in renewal rates between these subpopulations rather than the clonal expansion, and 5) that full telomerase compensation during clonal expansion is consistent with all data on the shortening of telomere length in, and between, naive and memory T cells. Thus we reconcile the apparent contradictions between the demonstrated difference in division rates between human naive and memory T cells and their similar rates of telomere shortening, and the demonstrated telomere shortening in the presence of telomerase activity.

Human T-cell responses after vaccination with the Norwegian group B meningococcal outer membrane vesicle vaccine

We have analyzed human T-cell responses in parallel with serum immunoglobulin G (IgG) antibody levels after systemic vaccination with the Norwegian group B Neisseria meningitidis outer membrane vesicle (OMV) vaccine. Ten adult volunteers, with no or very low levels of serum IgG antibodies against meningococci, received three doses intramuscularly of the OMV vaccine (at weeks 0, 6, and 46). T-cell proliferation against the OMV vaccine, purified outer membrane proteins (PorA and PorB), and control antigens (Mycobacterium bovis BCG vaccine and tetanus toxoid) was measured by thymidine incorporation of peripheral blood mononuclear cells before and after vaccination. The results showed that vaccination with OMV elicits strong primary and booster T-cell responses specific to OMV as well as the PorA (class 1) protein and significant, but markedly lower, responses against the PorB (class 3) protein. The median responses to OMV and PorA were 26 and 16 times the prevaccination levels, respectively. Most of the vaccinees showed low T-cell responses against OMV and PorA before vaccination, and the maximum T-cell responses to all vaccine antigens were usually obtained after the second vaccine dose. We found a positive correlation between T-cell responses and anti-OMV IgG antibody levels (r = 0.50, P < 0.0001, for OMV and PorA). In addition, we observed a progressive increase in the percentage of CD45R0+ (memory) CD4-positive T cells (P = 0.002). In conclusion, we have shown that the Norwegian OMV vaccine against meningococcal B disease induced antigen-specific T-cell responses, kinetically accompanied by serum IgG responses, and that vaccination increased the proportion of memory T-helper cells.

CD4+ and CD8+ cell cytokine profiles in neonates, older children, and adults: increasing T helper type 1 and T cytotoxic type 1 cell populations with age

The growing body of evidence suggestive of T helper types 1 and 2 (Th1/Th2) including their counterparts T cytotoxic types 1 and 2 (Tc1/Tc2) cell responses during various human disease states necessitates determination of normal T cell subsets' cytokine profiles. We show here, using intracellular cytokine staining and flow cytometry, that in healthy subjects interferon (IFN)-gamma producing CD4+ (Th1) and CD8+ (Tc1) cell populations progressively increase with age with strong correlation to CD45RO surface antigen expression. Meanwhile populations of cells capable of producing IL-4 (Th2 and Tc2) are comparably minimal across all age groups. Collectively, these results may reflect the maturation and expansion of Th1 and Tc1 cell populations from the neonatal period to adulthood, most probably dependent on antigen exposure.

Genes, immunity, and senescence: looking for a link

Aging is under the control of a small number of regulatory genes. Mice genetically selected for high immune responses, in most cases, exhibit longer life span and lower lymphoma incidence than do mice selected for low responses. The link between immunity and aging is further evidenced by the age-related alterations of the immune system, mostly of the T-cell population, in terms of replacement of virgin by memory cells, accumulation of cells with signal transduction defects, and changes in the profile of Th1 and Th2 type cytokines. Also, B cells exhibit intrinsic defects, and natural killer (NK) cell activity is profoundly depressed by aging. In vitro experiments indicate that IL-2, IFN-gamma, and IL-4 production by mouse spleen cells changes with aging and may be upregulated by recombinant cytokines. These findings suggest possible cytokine interventions to prevent or treat age-related immune disorders, as they may affect the duration and the biological quality of life.

Primary and secondary alterations of immune reactivity in the elderly: impact of dietary factors and disease

The function of the immune system declines with age. It is the aim of the present review to demonstrate that it makes sense to distinguish between primary and secondary alterations of immune reactivity in the elderly. Primary changes occur as the result of an age-dependent intrinsic decline of immune responsiveness. They also occur in healthy persons, i.e. persons selected according to the criteria of the SENIEUR protocol of the European Community's Concerted Action Program on Aging (EURAGE). T lymphocytes are hereby more severely affected than B cells or antigen presenting cells, possibly due to the involution of the thymus, which is almost complete at the age of 60. Secondary immunological changes occur as the result of environmental factors including diet, drug intake, physical activity etc. or are alternatively due to underlying diseases. In this article, the effects of high lipid intake as well as the impact of diseases, such as for instance Alzheimer's disease and atherosclerosis, will be addressed. The results underline the complexity of immunological alterations to be expected in old age. Changes in the aging immune system represent an opportunity for increased frequency and severity of disease and endanger the protective effect of vaccination.

Expression and catalytic activities of protein tyrosine kinases (PTKs) Fyn and Lck in peripheral blood T cells from elderly humans stimulated through the T cell receptor (TCR)/CD3 complex

Optimal signal transduction through the T cell receptor (TCR)/CD3 complex requires the coordinated activities of protein tyrosine kinases (PTKs) Fyn and Lck in addition to protein tyrosine phosphatases (PTPases) such as CD45. Although T cells stimulated with anti-CD3 monoclonal antibodies (mAb) exhibit age-related reductions in tyrosine phosphorylations of cellular proteins, it is unknown if the reduction represent abnormalities in PTKs or PTPases. In the current studies, immune complex kinase assays showed that the stimulation of peripheral blood T (PBT) cells from young humans with cross-linked anti-CD3 epsilon mAb OKT3 induced increased Fyn catalytic activity while anti-CD3 stimulation failed to induce significant increases in Lck activation. By contrast, Fyn activation in anti-CD3 stimulated PBT cells from a substantial proportion of elderly humans was reduced compared to anti-CD3 stimulated PBT cells from young humans. Also, we failed to find any increase in anti-CD3 stimulation of Lck activity in PBT cells from elderly subjects that could compensate for the decline in Fyn activity. However, no age-related alterations were detected in PBT cell expression of Fyn or Lck that might contribute to the changes in enzymatic activity. The results of other experiments demonstrated that the functional activities of PTPases in PBT cells from elderly subjects were equivalent to PBT cells from young subjects. These observations suggest that aberrant regulation of TCR/CD3 coupled PTKs may contribute to the age-related defects in signaling cascades and immune responsiveness of human T cells.

A shift to Th0 cytokine production by CD4+ cells in human longevity: studies on two healthy centenarians

Centenarians, particularly healthy centenarians, constitute the example of successful aging and the study of their immune status can help to define the endpoint of the changes occurring throughout life. We characterized T cell clones (TCC) of two healthy centenarians, studying their phenotypes and production of representative Th1 and Th2 cytokines (IFN-gamma and IL-4) and compared them with TCC obtained by three young normal subjects; in all 180TCC were analyzed. In young donors, 35TCC were CD4+, 56CD8+ and 2 were alpha beta +CD4-CD8- (double negative). In centenarians, we obtained 46CD4+TCC, 38CD8+, 2CD4+CD8+ (double positive) and 1 gamma delta + double negative. Of the young subjects' TCC, 71% produced IFN-gamma but no IL-4 (Th1 pattern) and this prevalence decreased to 39% in TCC from the centenarians. The number of clones showing the opposite Th2 pattern was similar in young and aged donors (3 out of 93TCC and 2 out of 87TCC, respectively). The intermediate profile of TCC producing both IL-4 and IFN-gamma (Th0) was found in 25.8% of clones from young people, but it almost doubled to 58.6% in centenarians. The analysis shows that the Th profiles of CD8+TCC is nearly superimposable in the two groups, whereas a major shift from a Th1 to a Th0 pattern is presented by CD4+TCC. The balance provided by a majority of CD4+TCC showing a Th0 pattern may ensure both humoral and cell-mediated defences. In CD8+TCC, however, a Th1 pattern still is present, possibly for efficient generation of cytotoxic responses. These findings should be extended by studying other centenarians and elderly subjects.