Aging and Immunity: Decrease in Interleukin-2 Production and Interleukin-2-Dependent RNA-Synthesis in Lectin-Stimulated Murine Spleen Cells

Stochastic non-enzymatic modification of long-lived macromolecules - A missing hallmark of aging

Damage accumulation in long-living macromolecules (especially extracellular matrix (ECM) proteins, nuclear pore complex (NPC) proteins, and histones) is a missing hallmark of aging. Stochastic non-enzymatic modifications of ECM trigger cellular senescence as well as many other hallmarks of aging affect organ barriers integrity and drive tissue fibrosis. The importance of it for aging makes it a key target for interventions. The most promising of them can be AGE inhibitors (chelators, O-acetyl group or transglycating activity compounds, amadorins and amadoriases), glucosepane breakers, stimulators of elastogenesis, and RAGE antagonists.

Ageing–apoptosis relation in murine spleen

Relatively few studies have been published with regard to modification of apoptosis in normal tissues as a function of ageing. The majority of these studies demonstrated an increase in programmed cell death (PCD) with age. However, opposite results, namely loss of apoptotic control with age, have also been reported. In the present study, we examined proliferation and apoptotic cell death in spleens of C57/BL mice of different ages. A tendency towards decrease in cell proliferative capacity was seen with age. By contrast, apoptosis was increased in spleens from aged animals. Moreover, the proliferative cell/apoptotic cell ratio decreased in function of age. Ladder type DNA degradation was much more pronounced in DNA derived from splenocytes of old mice. These results were supported by a decrease of Bcl-2 and an increase in Fas receptor expression as well as by increased activation of caspases 8, 3 and 9 in splenocytes from aged animals. In addition, cell surface molecular markers recognizable by macrophages in apoptotic cells, namely decreased sialic acid concomitant with increased unmasking of galactose residues, were more pronounced on splenocytes from old mice than on those from young animals. In addition to the experimental evidence which supports a role of apoptotic cell death in ageing, a series of theoretical reasoning, which could also favor this possibility, are discussed.

T-cell function in aging: mechanisms of decline

The above sections have provided numerous facts, many of which are conflicting, regarding the changes that occur with increasing age in T lymphocytes. Although it is impossible to state with absolute certainty the alterations that are responsible for decreased proliferation of lymphocytes from elderly subjects, the following summarizes the current status of the data: 1. The interaction of T lymphocytes with foreign stimuli appears to be generally intact. 2. Changes in numbers of CD3+, CD4+, or CD8+ cells before interaction with foreign stimuli or in the density of these markers or of mitogen receptors on the surface of aged T cells have not been consistently observed. When reported to occur, the changes are not sufficient to account for the significant decrease in T-cell proliferation that occurs with increasing age. 3. A defect in the ability of the membrane interaction with foreign stimulus to signal subsequent internal events may occur, because stimulation with phorbol esters and calcium ionophore can result in increased proliferation in some elderly subjects. 4. Decreased accumulation of cytosolic calcium after stimulation of elderly T cells occurs in mice and may be a major component of the defective activation system. This defect appears to be most apparent in the "memory" T cells (T cells expressing high levels of Pgp-1), which increase in number with increasing age. Decreases in Ca++ accumulation have not been observed in humans, but this may be due to different stimuli used. Further, investigation of an increase in "memory" T cells and of their inability to mobilize Ca++ has not been done in humans and rats. 5. Decreases in mRNA for c-myc, IL-2 receptor, and IL-2 have been reported in some, but not all, species. Whether these decreases are the result of decreases in Ca++ mobilization or are independent events in unknown. 6. Decreases in membrane expression of the activation marker RL388 and of TfR have been reported. 7. Lymphokines: a. Decreases in IL-2 production occur in mice and humans, but not in rats. In individuals with decreased IL-2 production, addition of exogenous IL-2 totally restores proliferative ability in only some individuals. Changes in IL-2R expression (number or affinity) may be an additional defect. b. Decreases in IFN-gamma occur in humans, but not in mice or rats. c. No change in IL-1 occurs in any species. Genotypic effects must be considered when evaluating the preceding observations. The heterogeneity among individuals, even within an inbred strain, cannot be discounted.(ABSTRACT TRUNCATED AT 400 WORDS)

In situ hybridization analysis of the age-associated decline in IL-2 mRNA expressing murine T cells

Only a small decrease in the number of L3T4- cells was observed in the Con A-stimulated splenocyte cultures of old mice as compared to young, which cannot account for the threefold decrease in IL-2 production. Northern and dot blot analysis of RNA from splenocytes containing equivalent numbers of L3T4+ cells from young and old mice showed that cells from old mice express less IL-2 mRNA after mitogenic stimulation than cells from young mice. Direct analysis by in situ hybridization of stimulated splenocytes from young and old mice then showed approximately a threefold decrease in the percentage of IL-2 mRNA expressing cells in the spleens of old mice as compared to young (8.7 +/- 4.1% old; 28.7 +/- 11.7% young). The average level of expression of IL-2 mRNA was not significantly different between cells from young and old mice; however, there were approximately 40% fewer cells expressing an intermediate to high amount of IL-2 mRNA in old mice as compared to young (26.3% vs 41.8%). These data suggest that the decrease in IL-2 production with age is associated primarily with a decrease in the frequency of IL-2 mRNA-expressing cells in old mice, especially in those cells expressing intermediate to high levels of IL-2 mRNA.

Decline in the production of interleukin-3 with age in mice

Previously, we and others have found that the ability to produce interleukin-1 (IL-1) and interleukin-2 (IL-2) declines with age in mice. The purpose of this study was to determine the influence of age on the capacity of mice to produce interleukin-3 (IL-3). Splenic cells (5 X 10(6)/ml) from young (3-4 months) and old (24-32 months) C57BL/6 mice were first assessed for their IL-3-producing capacities in response to varying doses of concanavalin A (Con A; 2-20 micrograms/ml) in a time-dependent manner. The results showed that the production of IL-3 by both young and old C57BL/6 mice was maximal on Days 3 and 4 in response to 20 micrograms/ml of Con A, and that of IL-2 was minimal (activity was less than 0.1 unit) on Day 4. Consequently, Day 4, was selected to assess the effect of age on IL-3 production by splenic cells. The results showed a twofold reduction in IL-3 production with age (P less than 0.05). Young-old splenic cell mixture experiments at ratios of 1:0, 3:1, 1:1, 1:3, and 0:1 indicated that the decrease in IL-3 production with age was not due to an increase in suppressor cell activity. Experiments based on mixtures of nylon wool-enriched splenic T-cell and adherent cells and on anti-MAC-1 plus complement-treated spleen cells indicated that (a) adherent cells are not required for T-cell production of IL-3, unlike IL-2 production, and (b) the decrease in IL-3 production with age is due solely to alteration in IL-3-producing T cells. Finally, a strong correlation was demonstrated between the production of IL-2 and IL-3 by spleen cells of individual young and old mice (r = 0.92, P less than 0.01). That production of both IL-2 and IL-3 is affected in a similar manner by age would suggest that a single class of helper T cells may be responsible for production of both lymphokines.

Pharmacologic immunoenhancement in the elderly: in vitro effects of isoprinosine

The loss of immune competence that occurs with aging may be responsible for increased morbidity and mortality in elderly individuals. Pharmacologic modulation of the immune response might reverse the immunologic aberrations associated with aging. We, therefore, investigated the effects of isoprinosine, an immunoenhancing drug, on selected in vitro immune responses in elderly subjects. Subjects studied were 65 years of age or older, and all had chronic diseases. We chose this population since they were at greatest risk for morbid events. Isoprinosine significantly enhanced mitogen-stimulated mononuclear cell proliferation, did not affect unstimulated cell growth, and needed to be present for the entire culture period for maximum effect. Isoprinosine is a potent in vitro immunoenhancing agent in aged humans.

Reversal by lymphokines of the age-related hyporesponsiveness to contact sensitization and reduced Ia expression on Langerhans cells

Contact sensitivity responses were evaluated in young adult (3-5 months) and aged (16-26 months) BALB/c mice which were systemically treated with interleukin-2 (IL-2), interferon-gamma (IFN-gamma) or saline. Mice older than 16 months of age have deficient numbers of Ia+ Langerhans cells in addition to their well-known impaired T cell functions. They also have an impaired cell-mediated response to contact sensitization with 1-chloro-2,4,6-trinitrobenzene. This hyporesponsiveness in aged mice can be almost completely reversed by IL-2 and is marginally improved by IFN-gamma. Exposure of skin from aged mice to interleukin-2 or interferon-gamma, both in vivo and in vitro, causes increases in the density of Ia+ Langerhans cells to levels approximating those in young mice. Since IFN-gamma causes partial restitution while IL-2 fully restores the contact hypersensitivity in aged animals, we conclude that the hyporesponsiveness in aged mice results both from defective Ia antigen expression on the antigen-presenting Langerhans cells and from deficient T cell function.

Proliferative and cytotoxic immune functions in aging mice. III. Exogenous interleukin-2 rich supernatant only partially restores alloreactivity in vitro

The ability of exogenous interleukin-2 (IL-2) rich supernatant to restore the defective T cell mediated immune functions of spleen cells from aged C57BL/6 mice was analyzed. Addition of IL-2 rich supernatant to allogeneic mixed lymphocyte cultures (MLC) resulted in an increase in the proliferative response of spleen cells from both young and old mice. The MLC response of cells from old mice was, however, not restored to the level of proliferation seen with splenocytes from young animals. In studying the generation of specific T cell suppressor function, it was found that IL-2 rich supernatant enhanced this function only for spleen cells from those aged animals which demonstrated a defective response in its absence. The response of these mice was thereby restored to the normal level. The response of cells from young control animals and aged mice with normal suppressor activity was not affected by the addition of IL-2 rich supernatant. We conclude that decreased IL-2 production constitutes a functionally important aspect, but is by no means the only defect in the immune response of aged mice. The results also suggest that responsiveness to IL-2 is less affected by age than lymphokine production.

Immunosenescence. Clinical and pharmacologic considerations

The effect of aging on the immune response is highly variable. Many individuals appear to maintain adequate immunologic function throughout life, whereas others have severely depressed immunologic responses accounting for disease activity. Both cellular- and humoral-mediated responses may be abnormal in the elderly. Aberrant function of immunoregulatory cells, effector T cells, and antibody-producing B cells contribute to poor immunity in the aged. Immunoenhancement in the elderly by pharmacologic agents appears promising. Several agents have been demonstrated to improve immune responses when administered to aging animals and humans. Although these studies are encouraging, it is not known if enhancement of immune responses in the elderly will be associated with clinical benefits. This issue must still be examined.