Tolerance induction as an index of age-related changes

Suppressor cells and their precursors in A/J mice, tolerant to heterologous gamma globulin

The role of suppressor cells and of their precursors was examined in A/J mice, immunized or tolerized-immunized with rabbit gamma globulin. Antibody response and tolerance were assessed by antigen elimination, followed by an indirect plaque-forming assay. Reconstitution experiments were performed to estimate loss of cooperative capacity in thymus and spleen cells. Infectious tolerance was examined by reconstitution with mixtures of spleen or thymus cells of normal and tolerant donors. Infectious tolerance could not be detected after neonatally induced tolerance. It could be detected when tolerance was induced 11-16 days after birth. Under these circumstances, loss of cooperative capacity and increased capacity for infectious tolerance occurred rapidly over the first 2 days and reached completion by the 10th-20th day after administration of tolerogen. Thymectomy, after tolerance induction, resulted in relative recovery of responsiveness of spleen cells and loss of capacity for infectious tolerance. Pretreatment with cyclophosphamide resulted in a less profound state of unresponsiveness and in the disappearance of the capacity for infectious tolerance. Simultaneous treatment with tolerogen and colchicine also resulted in a less profound state of tolerance. This effect of colchicine was more profound when a low dose of tolerogen was used or when animals were thymectomized before administration of tolerogen and colchicine.

Strain differences of age-dependent changes in the responsiveness to a T-independent type-2 antigen in mice

We have assessed age-associated early changes in antibody response to a T-independent type-2 (TI-2) antigen, dinitrophenylated ficoll (DNP-Ficoll). Mice of most strains, including long-lived and autoimmune-prone strains, give a high response when approximately 2 months old; thereafter the response declines sharply to the 3rd-4th month of age and continues to do so, more gradually, up to the age of 6 months. Age-related changes in the response of C57BL/6 mice follows a different course: the response remains unchanged up to the first year of life, i.e. to middle age. The in vitro anti-DNP-Ficoll antibody response of B cells could be increased by the addition of young syngeneic T cells. The augmenting activity of splenic T cells of C3H/He mice declines clearly as a function of age. In contrast, splenic T cells of C57BL/6 mice have low augmenting activity whether the T cells are obtained from young or middle-aged donors. Unlike the augmenting capacity of T cells, B-cell responsiveness to DNP-Ficoll increases until middle age in all strains examined. We conclude that early age-associated changes in antibody response to the TI-2 antigen is polymorphic and that the early age-related decline in in vivo responsiveness is attributable to an age-associated decline in augmenting T helper cell activity.

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.

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.

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.

Polymorphism of T- and B-cell sensitization by aggregate-freed heterologous gamma-globulin

Female A/J, C57BL/6J, SJL/J, MRL/MpJ-+/+, MRL/MpJ-lpr/lpr, NZB/BINJ and male BXSB/MpJ mice were injected at various ages with a tolerogenic form of rabbit gamma-globulin, or were left untreated and all were then immunized with dinitrophenylated rabbit gamma-globulin. We could distinguish 4 types of responsiveness to sRGG: (1) persistent T-cell tolerance (A/J, MRL/MpJ-+/+); (2) persistent T-cell tolerance and age-dependent resistance and sensitization of B-cells to tolerance induction (C57BL/6J, NZB/BINJ); (3) decreasing T- and B-cell tolerance (SJL/J, male BXSB/MpJ); and (4) T-cell sensitization in older animals (MRL/MpJ-lpr/lpr). Suppressor capacity and its regeneration was examined in terms of colchicine and cyclophosphamide treatment. Colchicine increased the immune response to a much greater extent in 10-week-old than in 6-week-old MRL/MpJ-lpr/lpr mice and had little effect on MRL/MpJ-+/+ mice. It had a relatively small effect on 15-week-old NZB/B1NJ and a much greater effect on 6-week-old animals. The reason for these differences are discussed.

Accelerated development of a Th-2 type factor in animals with and without an imbalance between help and suppression

A helper factor can be detected in antigen-treated supernatants from spleen T and adherent cells of sensitized animals. This factor promotes an indirect hapten-specific plaque forming response of B cells, irrespective of the identity of the carrier, i.e. provides the Th-2 type of help. Factor production increases with age and occurs most rapidly in strains known to have an accelerated decrease of suppressor capacity. The reason for the inverse correlation between suppressor capacity and the Th-2 type of helper factor is discussed.

Mechanisms involved in age-dependent decline of immune responsiveness and apparent resistance against tolerance induction in C57BL/6 mice

The plaque-forming antibody response of C57BL/6 mice to rabbit gamma globulin (RGG) decreases as a function of ae. RGG in tolerogenic form induces tolerance of young mice but sensitizes older animals. If antigen is administered together with lipopolysaccharide, the age-dependent decline in immune responsiveness is not observed, nor are older animals sensitized by tolerogen. The age-dependent decline in immune responsiveness is due to a loss of T helper capacity; sensitization by tolerogen is attributable to a subpopulation of B cells which becomes sensitized by the tolerogen. Older animals, treated with tolerogen, show a degree of central tolerance of T cells and a relatively slight, age-dependent diminution in colchicine- or cyclophosphamide-sensitive precursors of suppressor cells.

Accelerated development of Th-2 type of helper effect in MRL/MpJ-lpr/lpr and BXSB/MpJ mice

Age-dependent changes, during adult life, in suppressor capacity and B cell responsiveness have been known for some time. In this paper, an age dependent change in helper function, is being reported. A Th-2 type of helper effect can be observed in tissue culture of spleen cells from animals sensitized with a macromolecule. An indirect plaque-forming response to the hapten occurs when the spleen cells are exposed to the sensitizing macromolecule and to the hapten conjugated to a carrier, structurally unrelated to the sensitizing macromolecule. There is considerable polymorphism in the age at which this effect is first demonstrable and at which it reaches mature levels. Mice of inbred stains, with various defects in the suppressor cell circuit (SJL/J, MRL/MpJ-lpr/lpr, BXSB/MpJ show an accelerated development of Th-2 helper capacity in the indirect plaque-forming response.

Diversity of age-dependent changes of antibody formation and of tolerance decrease

Age-dependent changes in immune response and in tolerance occur at different rates in inbred mice of different genetic backgrounds. The change in tolerizability is connected with the change in the balance of the suppressor helper circuit; the change in B-cells, at least in C57BL/6 mice, appears to be also due to a regulatory change. Changes in immune responsiveness and tolerance inducibility appear to vary independently of one another.

Resistance of MRL/Mp-lpr/lpr mice to tolerance induction

Mice of strain MRL/Mp-lpr/lpr develop resistance against tolerance induction with aggregate-freed rabbit gamma-globulin as early as 6 weeks of age and show very complete resistance when they are 10 weeks old; congenic mice MRL-Mp+/+ of 6 and 10 weeks can be rendered tolerant. By reconstitution experiments, it was shown that T cells from MRL/Mp-lpr/lpr are responsible for the resistance to tolerance induction. A cell which is not colchicine-sensitive contributes to tolerance of MRL/Mp-+/+, but not to MRL/Mp-lpr/lpr mice. Resistance of T cells against tolerance depends on expression of the lpr gene.

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

The thymus of SJL/J mice of age 3-6 weeks has been previously shown to contain suppressor cells that inhibit the antibody response to lymph node cells to SRBC. The effect of these suppressor cells disappear as the animals age (24 weeks or more). We find that these aged animals acquire thymic suppressor cells which suppress the generation of cytotoxic T-cells both in vitro and in vivo. Although such suppressors are not present in the thymuses of young SJL/J mice, suppression can be induced by treatment with estrogen and progesterone. The differentiation of functionally different suppressor cell populations in thymus may be affected by both age and hormonal status.

Effect of 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin) on tolerance induction in SJL mice

The effect of 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin) on tolerance induction with rabbit gamma globulin (RGG) was investigated. The treatment with ribavirin, initiated on the 4th and 17th day of life, did not reduce the immune response significantly, but provided a much more profound level of tolerance than could be achieved in animals not treated with ribavirin. When treatment with ribavirin was initiated at the age of 50 or 65 days, the response of immunized animals was reduced and the response of tolerized-immunized animals was increased. The mechanism, underlying the drug action, was discussed in terms of an effect or ribavirin on the balance between help and suppression; the possibility that a virus may be involved in age-dependent changes and that ribavirin prevents it proliferation, was considered.

A strain survey of age-dependent changes in antigen elimination, antibody formation and tolerance

A strain survey has been undertaken to examine polymorphism of age-dependent changes in antigen elimination, immune responsiveness and tolerance inducibility. In young mice of tested strains, other than C57BL/6J, aggregate-freed mouse Ig was eliminated faster than was the xenogeneic Ig(RGG); C57BL/6J was the only exception. The rate of elimination increased with age in all strains, tested. Antibody formation to RGG decreased in 3 (BALB/cJ, 129/J, DBA/2J) out of the eleven strains tested at 5--7 and 31--40 weeks of age; there was a considerable strain variation in the extent of this decrease. Age-dependent resistance to tolerance induction was observed in a fraction of animals of H-2 haplotypes, H-2k and H-2d.

Accelerated age-dependent decline in the T suppressor capacity of SJL mice

Tolerance induction with rabbit gamma-globulin was employed as a probe for age-dependent changes in suppressor capacity of SJL lymphoid cells. The tolerant state was assessed by loss of cooperative capacity and by infectious tolerance. The supply of precursor cells was assessed by thymectomy and by treatment with colchicine and cyclophosphamide, which have been reported to eliminate suppressor cells. Thymectomy, 16-18 days before tolerance induction, did not affect antibody response or tolerance inducibility; thymectomy, 33 days before tolerance induction, reduced both antibody response and tolerance inducibility. Colchicine, injected together with aggregate-freed rabbit gamma-globulin, inhibited tolerance induction partially in 35-day-old mice and completely in 106-day-old mice. Colchicine, given to younger mice, thymectomized 17 days before tolerance induction, prevented tolerance induction completely. A low dose of cyclophosphamide interfered with tolerance induction in older, but not in younger mice. A high dose of cyclophosphamide interfered with tolerance induction in thymus cells of younger and older mice. After thymectomy, there was a much more profound interference of a low dose of cyclophosphamide with tolerance induction. Results were discussed in terms of an age-dependent decline of thymus progenitors and of peripheral progenitors of suppressor cells.

Resistance of SJL mice to immunosuppression by antibodies

Immunosuppressive antisera that specifically inhibit induction of tuberculin-type delayed hypersensitivity in mice to the antigens chicken conalbumin and methylated human serum albumin were compared for activity in CF-1, CAF1, and SJL mice. These contrasensitizing antisera were effective in CF-1 and CAF1 mice of various ages. But in SJL mice they were ineffective if the animals were older than 8 weeks and were only moderately effective if the animals were younger. The antibodies of these antisera responsible for specific immunosuppression could be absorbed onto adherent peritoneal exudate cells taken from DAF1 but not SJL mice. They could be eluted from the CAF1 cells at 56 degrees C. These results and other data that are discussed suggest that SJL resistance to immunosuppression by contrasensitizing antibodies is related to a macrophage abnormality. The results also help explain earlier findings that SJL mice are unusually easy to sensitize and unusually resistant to tolerogenesis. This strain of mice should be especially useful for studying the mechanisms of afferent immunosuppression in immunologic enhancement-like forms of tolerance.