Age-dependent separation of class-specific suppressor cells in thymus of SJL/J mice

Aging. Polymorphism, compartmentalization and environmental impact

The proportion of elderly in our population is steadily increasing and so is the need to provide sophisticated health care. We must intensify research which provides results, leading to the design of preventive medicine, before the increased proportion of aged causes a crisis in our health care and social systems. The potential impact of such research represents the best and most cost-effective means of preparing for the future, and providing directions for a better quality of life with reduced chronic and debilitating illness for the elderly. Indeed, prevention appears to be the only approach able to lower the enormous economic burden of the cost of geriatric medicine [1,2]. There are many precedents in medical research for preventive measures being much more cost-effective than therapeutic means: one of them is immunization against poliomyelitis as an alternative to development of improved models of iron lungs.

Polymorphism of age-related changes in the antibody response to the hapten phosphorylcholine

Aging is accompanied by changes in the immune system that occur at different levels and at different periods of time. We have studied age-related changes in isotype and idiotype of the antibody response to hapten phosphorylcholine (PC) in C57BL/6, and A mice and in the congenic MRL/Mp(-)+/+ and MRL/Mp-1pr/1pr strains. Three groups, representing young, middle and old age were immunized with PC-keyhole limpet hemocyanin. Total anti-PC antibody and the contribution of each isotype and of the T15 idiotype were assessed in the initial and late response. Some features of the antibody-response were similar in all the strains tested, e.g. the largest quantity of anti-PC antibody is formed in middle age and IgM is dominant in the initial response. However, remarkable differences occur in the isotype and idiotype predominance. Particularly, congenic MRL/Mp strains, prone to autoimmune disease, express the T15 idiotype only at low levels, even though IgM, which normally expresses this idiotype, is produced in large amounts. Furthermore, the late (memory) response of the MRL/Mp strains is dominated by IgG2b rather than IgG1, which is the predominant isotype in mice of long-lived strains. We conclude from these results that the number of T helper cells, involved in isotype regulation decreases with age and that there is a genetic variation, i.e., polymorphism in the ability to express T15-idiotype producing subtypes.

Polymorphism of age-related changes in interleukin (IL) production: differential changes of T helper subpopulations, synthesizing IL 2, IL 3 and IL 4

Inbred mice were examined for strain differences in age-associated changes in the capacity to synthesize interleukin (IL), i.e. IL 2, IL 3 and IL 4 after stimulation with phorbol myristate acetate (PMA) and calcium ionophore (A23187). Production of IL 2 remains constant in A/J, DBA/1 and DBA/2 mice and decreases with age in one of the strains examined (C57BL/6J). Strain differences in age-associated change of synthesis did not show the relation between youthful synthetic capacity and magnitude of later decrease ("economic correction") which is observed in several other systems. This difference between different types of polymorphisms is attributed to an age-associated defect in intrinsic capacity to synthesize IL 2 which may occur in only one of the tested strains, C57BL/6J. In contrast to IL 2 production, the quantities of IL 3 and IL 4 increase progressively, with advancing age, in mice of the three strains tested. T cells from old mice contain a greater frequency of cells producing IL 3, than do those of young mice. In addition, synthesis of IL 3 is induced at a relatively lower concentration of PMA in cells from old animals and this may be a consequence of different signal requirements of the two subsets of the T helper cells, but also a change in intrinsic properties of these cells. Since IL 3 and IL 4 production, but not IL 2 production, increases with age, it is reasonable to conclude that this reflects an expansion of a T helper cell population which secretes IL 3 and IL 4, but not IL 2, presumably TH2.

Strain polymorphism in progression of aging: changes in CD4, CD8 bearing subpopulations

Polymorphism of age-related changes in CD4 (L3T4) and CD8 (Lyt-2) determinants of spleen and thymus cells was assessed by fluorescence-activated flow cytometry. Cells from mice ranging from 5 weeks to greater than 2 years of age were examined. There is little age-related change in the proportion of CD4+ CD8- splenocytes in A, C57BL/6, DBA/1, DBA/2, and SJL mice (slopes 0.04, 0.06, 0.08, 0.17 and 0.17, respectively, when age in weeks was plotted against % of positive cells). Changes in the composition of the thymus are much more profound: CD4+ CD8+ cells of SJL mice decrease from 70% to less than 10% as the animals age from 5 to 69 weeks (slope -1.03), and in DBA/2 mice from 5 to 110 weeks (slope -0.88). While this decrease in CD4+ CD8+ cells occurs, there is a compensatory increase in CD4+ CD8- and CD4- CD8+ cells; this is a shift in the relative proportion of subpopulations rather than an increase in absolute cell numbers of a particular subpopulation. In contrast to the age-related changes of SJL and DBA/2 mice, there is relatively little change in the proportion of CD4+ CD8+ thymus cells in mice of strains C57BL/6, DBA/1 and A (slopes -0.03, -0.14 and -0.15, respectively).

Age-related changes in contact photosensitivity differ among mouse strains

There are differences among mouse strains in the age-related changes in reactivity to the contact photosensitizer tetrachlorosalicylanilide (TCSA). We found a tendency to lower reactions in older mice, with some strains showing declines from an early age (BALB/cJ, MRL/MpJ +/+, MRL/MpJ lpr/lpr and SJL/J). Others had increasing reactions until about 30-50 weeks of age before declining (DBA/1J, C3H/HeJ, and A/J) and one strain (C57BL/6J) had increased reactivity with age. There are also differences in the role of cyclophosphamide-sensitive T-suppressor cells in these age-related changes. In some mouse strains, BALB/cJ, C57BL/6J, A/J, DBA/1J and C3H/HeJ, age-related changes in reactivity to TCSA are independent of changes in cyclophosphamide-sensitive suppressor cells. In other strains, MRL/MpJ +/+, MRL/MpJ lpr/lpr and SJL/J, the development of cyclophosphamide-sensitive suppressor cells is responsible for the initial, though not later, stages of the age-related decline in reactivity.

Effect of dietary fat on antibody response and on down-regulation

Diets differing in the ratios of polyunsaturated to saturated fatty acids (P/S) have dramatically different effects on the extent to which pretreatment with aggregate-freed form of a foreign protein augments or diminishes (by sensitization or down-regulation) the subsequent response to an immunogenic form of the same protein. We have examined this phenomenon in terms of both down-regulation (acquired immunological tolerance) and sensitization induced in 87-week-old female C57BL/6 mice. Antibody response in these mice, fed on low P/S diets, could be down-regulated by pretreatment with aggregate-free rabbit gamma globulin, as manifested by antibody to aggregated rabbit gamma globulin of isotypes IgG3 and IgG2b. Animals fed high P/S diets were not down-regulated by the pretreatment, but were sensitized; there was a 2-3-fold increase in IgG3, IgG1, IgG2a and IgA antibody to rabbit gamma globulin.

Antibody response and acquired tolerance of A/J mice: age- and immunogen-related isotype differences

In earlier work we have observed strain- and age-related diversity of immunological ageing in inbred mice pretreated with tolerogen or left without pretreatment and then immunized. Different isotypes show different age- and strain-related changes. Here, we extend this isotype analysis from C57BL/6 and SJL to A/J. By comparison with the first two of these, animals of strain A/J show very little age-related change, as judged by indirect plaque-forming response. We have found that in A/J, as in SJL and C57BL/6 mice, age-related changes are isotype-dependent. The age-related changes in isotype predominance and magnitude differ for different determinants. They depend on the structural relation between the tolerance-inducing or -sensitizing macromolecule and the immunogen.

Developmental change in the second half of life--strategies for modification of selected compartments of aging

Age-related changes of different individuals multicentric and polymorphic. We have approached this problem of age-related changes by examining (1) membrane densities of receptors of various ligands in different organs, and (2) changes in different classes of T cells and of antibody response. Three strategies have been developed to modify progression of age-related changes to different extents in different compartments in which age-related changes occur. The first is based on administration of hormones, the second on administration of purine analogues and the third on administration of diets which differ in fatty acid content. Details of this last approach are reviewed in this paper. Lifespan of different species is a component of the evolution of each species. The variables which are decisive in the evolutionary processes which affect lifespans of different species are not necessarily variables which play a decisive role in the different health span of different individuals of the same species. For each individual of a given species, relative health span represents variations within the limits of the evolved lifespan of the species and depends on alleles of many different genes.

Cyclosporine and the thymus: influence of irradiation and age on thymic immunopathology and recovery

With the proper experimental conditions, previous studies have demonstrated that syngeneic and autologous radiation chimeras treated with cyclosporine (CsA) routinely develop a syndrome resembling graft-vs-host disease (GVHD) after CsA is discontinued. The thymus is clearly important in the pathogenesis. Thymectomy prior to CsA prevents the development of syngeneic GVHD and the process can be adoptively transferred via thymocytes. The thymus, however, must be within the field of irradiation and the animal must be young. Here we examine how irradiation and advanced age influence the thymic immunopathologic changes induced by CsA and influence the recovery post-CsA. Young LEW rats, with or without pre-CsA mediastinal irradiation, demonstrate a marked involution of the thymic medulla with associated loss of medullary epithelium, Hassall's corpuscles, class II antigen expression, and maturation of thymocytes. While the control group underwent rapid and complete regeneration of the medulla post-CsA, however, the medullary changes in the irradiated group were prolonged or permanent. Most of these animals had changes of chronic GVHD. Older LEW rats had a more prominent medulla prior to CsA. In contrast to younger rats, the medulla did not show significant involution with CsA. While the Hassall's corpuscles disappeared, the medullae still had fusiform epithelium, dendritic cells, and class II antigen expression. Phenotype stains demonstrated many mature-appearing CD4+/CD8- lymphocytes. In light of evidence indicating the importance of the medullary microenvironment to the maintenance of self tolerance, the medullary effects of CsA are most likely essential to the development of autoimmunity. Young rats rapidly lose the ability to maintain tolerance. While unirradiated rats rapidly reestablish the proper microenvironment following CsA, irradiated rats have a prolonged loss. Older rats may resist the development of autoimmunity by retaining the medullary microenvironment.

Lymphokine-activated killer (LAK) cells: I. Age-dependent decline of LAK cell-mediated cytotoxicity

Experiments were designed to assess age-related changes in generation of lymphokine-activated killer (LAK) cells and to test whether these changes can be modified by diets differing in the proportion of polyunsaturated to saturated fatty acids (P/S). Ficoll-Hypaque-isolated spleen lymphocytes of rodent chow-fed, 6-85-week-old C57BL/6 (H-2b), 8-81-week-old C57BL/10 (H-2b) and 6-62-week-old SJL (H-2s) mice were cultured in IL-2-containing medium and examined in 51Cr cytotoxicity assay. Similarly, Ficoll-Hypaque-isolated spleen lymphocytes of 6-36-week-old SJL mice fed diets which differed in the ratio of polyunsaturated/saturated fatty acids were cultured in IL-2-containing medium and assayed for cytotoxicity. Age-related decline of LAK cell-mediated cytolysis was observed in mice of both H-2b and H-2s haplotype. The age-related decline of LAK cell-mediated cytolysis was the consequence of age-related decrease in the rate of LAK cell precursor maturation. SJL mice fed from birth with diets differing in P/S did not differ in LAK cell-mediated cytolysis.

Polymorphism of age-related changes in stimulatory capacity of murine dendritic cells

All through life, regulatory and executive components of the immune system undergo changes, differing in rate and extent, dependent on the genetic background. We have, here, examined age-dependent changes in stimulatory capacity of dendritic cells (DC) in allogeneic mixed leukocyte reaction (MLR). DC of mice of five strains showed very little change as they aged. DC from mice of two other strains showed a significant age-related decrease of stimulatory activity and those of one strain showed an increase. The capacity of DC to stimulate syngeneic MLR was examined in three strains, as a function of age, and was found to decrease in one and to slightly increase in two. The underlying cause for this extensive polymorphism remains to be determined. We could not find supporting evidence for the view that the observed changes were related to changes in Ia density on dendritic cells.

Age-related changes in beta-adrenoceptors of lymphocytes

The density of adrenoceptors (Bmax) is greater on B than on T splenocytes. It decreases more or less rapidly on membranes of both populations, as animals age. The exception, we have observed in this respect, is an increase in Bmax on B cells of SJL mice, between the 6th and 25th week of life.

Dietary fat alters progression of some age-related changes of the immune system

SJL mice develop resistance against tolerance between the 9th and 25th wk of life. This resistance is linked with a loss of suppressor capacity in the thymus. We have shown here that contact photosensitivity (CPS) decreases as a function of age and that this is due to an age-dependent increase in suppressor capacity. Diet fats have a differential effect on age-dependent changes in suppressor activity; a low P/S diet prevents or delays loss of suppressor activity for antibody formation and a high P/S diet prevents or delays the development of suppressor activity in CPS reactions.

Immune response, tolerance circumvention and autoantibodies in aging MRL/Mp-lpr and MRL/Mp-+ mice

Isotype distribution was analyzed, as a function of age in MRL/Mp-lpr and MRL/Mp-+ mice. The mice were tested for: (1) "spontaneous" response to nucleic acid (2) induced response to alum-precipitated phosphorylcholine-rabbit gamma globulin (PC-RGG) (immunized animals) and (3) induced response to alum-precipitated PC-RGG after pretreatment with aggregate-free RGG (tolerized-immunized animals). "spontaneous" nucleic acid antibodies of isotypes, other than IgM, increased as animals became older. The quantity of RGG antibody declined as a function of the age at which animals were immunized. Young tolerized-immunized animals made less antibody of all isotypes than did immunized animals. In later life, resistance against tolerance induction developed. Aggregate-free RGG sensitized older animals and, thus, augmented the response to alum-precipitated PC-RGG. Up to the age of 20 weeks, spontaneous antibody and antibody of tolerized-immunized animals showed striking similarities in age- and strain-dependent changes of IgG2b and IgA isotypes. Results were discussed in terms of: (1) a defect in down regulation of immune responsiveness, which contributes to the initiation of autoimmunity and age-dependent resistance to tolerance induction; (2) regulatory mechanisms for isotype switching, which contribute to resistance to tolerance induction, whether naturally occurring or experimentally induced; and (3) age-related immunological changes which are inherent in the MRL/Mp genome, the mutant gene, lpr/lpr, accelerating the changes.

Strain-dependence and cellular aspects of the acceleration of age-dependent shift in class-specific helper and suppressor activity in the thymus of MRL/Mp mice by the LPR gene

Previous studies of the immunoregulatory activity of thymocytes from SJL/J mice have shown loss of suppressor activity for the antibody response by 24 weeks of age with appearance of helper activity. At the same time, suppressor cells developed which inhibit the generation of cytotoxic T lymphocytes (CTL). We now show a similar pattern of helper and suppressor activity in MRL/Mp mice. Presence of the lpr/lpr genotype significantly accelerated the onset of these changes in thymocyte activity. A similar pattern of thymocyte activity was not detected in C57B1/6 mice. In aged MRL-lpr mice, evidence of increased suppressor cell activity for the CTL response could be demonstrated in spleen, and the suppressor was sensitive to treatment with anti-thy 1.2 + complement. The magnitude of the deficiency in the CTL response in MRL-lpr mice was greater than could be accounted for by suppressor cell activity alone. Measurement of the frequency of CTL precursors (CTLP), the yield of CTL per CTLP, and the ability to produce and to respond to interleukin 2 (IL-2) indicated that a drop in CTLP frequency, subnormal generation of IL-2, and probably an intrinsic defect in the responsiveness of MRL-lpr CTLP to IL-2 was contributing to the defective CTL response. We were not able to link suppressor T cells with reduced responsiveness to IL-2. Ageing involves different patterns of change in immunoregulatory T-cell subsets in different strains of mice, depending on their genetic constitution. The general implications of this conclusion for prediction of immune dysfunction with age in genetically distinct members of an outbred population are discussed.

Effect of thymus grafts of various ages on the immune system formation in CBA mice

An attempt has been made to govern the development of immunological capability in CBA mice by means of transplantation at an early postnatal period of thymus from donors of various ages. The results have shown that in thymectomized animals, apart from a well known gradual decline with the donor's age in restorative functions of the transplanted thymus, there was at the age of 22 months a phase of inhibitory influence on the recipient's immune system. In intact animals, transplantation of the thymus from a 5-day-old donor caused a decrease and that from a 22-month-old donor caused an increase in the development of the capacity for immune response. Taken together, our findings indicate an active role of the thymus both in the formation of the immune system and in its alteration with aging.

Sensitization of T and B cells by a normally tolerogenic macromolecule: the induction of unresponsiveness and of sensitization is polymorphic

Changes induced in B and T cells by tolerogen were experimentally defined in animals which resist down-regulation. Female A/J, C57BL/6J, MLR/MpJ-lpr/lpr, MLR/MpJ-+/+ and NZB/B1NJ mice were injected at various ages with a tolerogenic form of rabbit gamma globulin (sRGG) or were left uninjected, and all were then immunized with dinitrophenylated RGG (DNP-RGG) on alum. The degree of tolerance was estimated by measuring anti-DNP and anti-RGG spleen plaque-forming cell (PFC) numbers. In some cases, the state of T or B cells deduced from these experiments was further examined by cell transfer experiments. Four types of responsiveness to the tolerogenic form of RGG (sRGG) were distinguished: 1) persistent tolerance inducibility of T and B cells to tolerance induction (A/J); 2) T cells retaining tolerance-inducibility after initiation of age-dependent sensitization of B cells by the tolerogenic form of RGG (C57BL/6J, NZB/B1NJ); 3) age-dependent resistance of T cells to tolerance-induction and age-dependent sensitization of B cells by tolerogen, with the sensitization only manifesting itself in reactivity with T cells from immunized donors (SJL/J); and 4) sensitization of T cells by a usually tolerogenic form of RGG (MLR/MpJ-lpr-lpr). Thus, the development of resistance against tolerance induction is highly polymorphic, not only with respect to the age of onset, but also with respect to the cellular site of its first manifestation and the effect. Possible mechanisms of B-cell sensitization in sRGG-treated C57BL/6 and NZB mice are discussed in relation to the age-dependent emergence of a B-cell subpopulation and of non-specific helper T-cell factors.

Aging and the immune system

Information is presented on changes in the aging immune system. An analysis of separate streams of cellular aging in the inbred mouse is presented. It is demonstrated that there is extensive polymorphism in the aging of different types of executive and regulatory cell lines.

Sensitized spleen B-cells in tolerance-resisting SJL mice

A subpopulation of B-cells becomes sensitized in the 15-week-old SJL mouse, exposed to aggregate-freed rabbit gamma-globulin, which is highly tolerogenic when given to younger animals. This state of activation can only be expressed in collaboration with sensitized T-cells. The sensitized B-cell does not play an important role in the response of the intact 15-week-old SJL mouse, since there are no sensitized T-cells in the sRGG-treated animals.