Immune response in aged mice. Change of cell-mediated immunity with aging

The effect of age, sex and breeding on graft versus host reactivity of spleen cells from C57BL mice

Spleen cell graft versus host (GvH) reactivity was determined in male and female, either virgin or breeder, C57BL mice from 3 to 24 months of age. The GvH reaction was assessed by a local popliteal lymph node assay and by a splenomegaly test for a systemic reaction. Although the GvH reactivity declines progressively with age in both sexes the virgin female response was greater than that of males throughout the period of 6-18 months of age. Two-year-old mice of both sexes were practically unable to mount a GvH reaction. No differences were evident in aging female reactivity after one or two syngeneic pregnancies. On the other hand, 3 or more consecutive pregnancies resulted in enhanced GvH reactivity of 12-24-month-old females, which responded comparably to young virgin mice. This long-lasting immunopotentiating effect of multiparity was similar after 3-4 and 8-9 pregnancies. The possible role of developing foetuses on the maintenance of high GvH reactivity in breeder females is suggested.

Thymectomy at weaning. An accelerated aging model for the mouse immune system

Mouse thymectomy at weaning induces a long lasting immunodepression which can be measured by in vivo and in vitro experiments. Lymphocyte proliferation and IL2 production in response to a T cell mitogen are greatly diminished during the whole life of the animals, on the contrary B cell proliferation in the presence of lipopolysaccharide is not modified. The lack of effect of surgery on the in vitro T cytotoxic activity compared to the total abolition of in vivo graft versus host reaction shows that these two phenomena are under the control of different immunocompetent cell subsets. Thymectomy induces a stabilization of natural killer cell activity, while during normal aging, this parameter decreases regularly. Surprisingly, the thy 1+ cell level is normal 8-10 months after thymectomy compared to sham operated animals showing that phenotypically normal cells can be dysfunctional. Macrophage activity is not modified either by aging or by thymectomy. So, thymectomized mice can be used after less than 1 year to study immunopharmacology of aging.

Restorative effect of neurotropin on maturation of bone marrow cells to IL-2-producing T-cells in aging BALB/c mice

In a previous paper, we have demonstrated that Neurotropin, a non-protein extract isolated from the inflamed skin of rabbits inoculated with vaccinia virus, restores decreasing immune responses through the recovery of interleukin-2 (IL-2) production in aging BALB/c mice. To clarify the mechanism by which Neurotropin restores IL-2 production, its effect on the recruitment of IL-2-producing T-cells from bone marrow cells was examined using syngenic radiation bone marrow chimeras. Two fundamental lesions in recruiting IL-2-producing T-cells in aging BALB/c mice were demonstrated: (1) a drastic decline of the maturation of bone marrow cells to IL-2-producing T-cells as demonstrated by old----young chimeras; and (2) an environment unable to support bone marrow cell differentiation to IL-2-producing T-cells by young----old chimeras. Neurotropin clearly restored the maturation of bone marrow cells to IL-2-producing T-cells when administered from 13 to 16 month-old mice, whereas the non-complementing environment was not normalized with Neurotropin administration. These results suggest that Neurotropin administration restores IL-2 production through the recovery of the maturation of bone marrow cells to IL-2-producing T-cells, resulting in restoration of in vivo T-cell immune response in aging BALB/c mice.

Ultimate erythropoietic repopulating abilities of fetal, young adult, and old adult cells compared using repeated irradiation

Erythropoietic repopulating abilities of fetal liver cells and young and old adult marrow cells were compared as follows: Equal numbers of cells from a donor of each age were mixed with a constant portion of cells pooled from genetically distinguishable competitors. These mixtures were transplanted into stem cell-depleted recipients, and the proportions of recipient hemoglobin that were donor type measured the relative effectiveness of early erythropoietic precursor cells from the various donors (Fig. 1). At intervals of 3-6 mo, recipients were sublethally irradiated, requiring a new round of competitive repopulation. When B6 mice were used as donors, with WBB6F1 competitors and recipients, the highest levels of stem cell activity were found using old donors (Tables I, III). This was true even with unirradiated, immune-competent W/Wv recipients (Table III). When donors and recipients were WBB6F1 hybrids, with B6 competitors, fetal cells initially gave higher levels of repopulating ability, and they were similar to the adult and old marrow cells after 400 d and after recovery from two sublethal irradiations (Table II). These effects were mostly insignificant and probably reflect small differences in initial stem cell concentrations that are brought out by the sensitivity of the competitive repopulation assay. Clearly, ultimate erythropoietic stem cell proliferative capacities did not decline as a result of the proliferation required between 15 d of fetal life and old age. Repopulating abilities of 12-d fetal liver cells were not detectable. We also showed that the proportions of newly synthesized hemoglobins made by the two types of stem cells in tetraparental mice remained nearly constant when tested at 3-d intervals over 30 d. Minimum numbers of stem cells producing erythrocytes over a single 3-d period were calculated as 62 and 128, but these are too low, since variances were similar in the tetraparental mice and in the F1 hybrid control. This contradicts the hypothesis that erythropoietic stem cells reserve limited proliferative capacities by proliferating one or a few at a time. We suggest that erythropoietic stem cells have essentially unlimited proliferative capacities and are found in approximately equal concentrations in the primary erythropoietic organs after 15 or 16 d of fetal life.

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.

Long-term erythropoietic repopulating ability of old, young, and fetal stem cells

It is possible that erythropoietic stem cells do not age. This would mean that stem cells from old donors can function as well as those from young or fetal donors. The competitive repopulation assay has been used to test long-term stem cell function by directly comparing how well competing stem cells repopulate a recipient and produce differentiated cell types. C57BL/6J (B6) mice were used as donors, while recipients and competitors were WBB6F1 hybrids with genetically distinguishable hemoglobin. Lethally irradiated young WBB6F1 recipients were given a mixture of 2.5 X 10(6) cells from B6 old marrow, young marrow, or fetal liver donors; each recipient also received a standard dose of 1 X 10(6) marrow cells from a pool of young WBB6F1 competitors. Surprisingly, the old marrow cells competed the best in repopulating the recipients. This pattern was maintained even after recovery from sublethal irradiation, a treatment that severely stresses stem cells. This stress was demonstrated when sublethal irradiation caused a 20-fold decline in repopulating ability measured using hemoglobin markers, and a 3- to 7-fold decline using chromosome markers. Stem cells from old marrow competed better than young or fetal cells in similar experiments using immunologically crippled recipients or using unirradiated W/Wv recipients that are immunologically intact. In both types of recipients, the advantage of old marrow cells again persisted after recovery from sublethal irradiation. Other genotypes were tested, and marrow cells from old B6CBAF1 donors competed better than those from young donors of that genotype. However, marrow cells from young CBA donors completed better than those from old CBA donors. These results support the hypothesis that stem cells do not age, and suggest that regulatory changes with age promote rapid stem cell repopulation in B6 and B6CBAF1 mice, but inhibit it in CBA mice.

Alteration in lymphocyte recognition repertoire during aging. II. Changes in the expressed T-cell receptor repertoire in aged mice and the persistence of that change after transplantation to a new differentiative environment

Changes in the T-lymphocyte alloreceptor repertoire associated with aging by exploring the frequency of cytotoxic T-lymphocyte precursors (CTLp) available for activation by various major histocompatibility complex (MHC) haplotypes in mice of different ages have been investigated. There was no consistent pattern of change in CTLp frequencies. Thus, for instance, while the frequency of responder C57B1/6 CTLp for ATH alloantigen decreased with age, the frequency for C3H alloantigen increased. There was no significant change in the overall frequency of splenic CTLp (assessed irrespective of antigen specificity). No evidence was found that CTL produced by activated CTLp of aged mice were less specific in their lytic capacity that CTL produced by CTLp of young mice. However, by assaying responder CTLp cultures at limiting dilution we obtained evidence that the "burst size" (mean lytic capacity per responder well assayed at limiting dilution) was diminished with age of the donor of the CTLp pool. Furthermore, we obtained evidence that the apparent affinity of CTL for their target antigen was consistently decreased when those effector cells were derived from a pool of CTLp of aged mice. All of these changes reflected in mature T cells derived from aged mice were already apparent in the bone marrow stem cell pool of aged individuals and were not due to environmental influences alone, as assessed by the phenotype of T cells derived from young or old bone marrow stem cells transplanted to young or aged recipient mice. A final study has examined evidence for more subtle changes in the T-cell alloreceptor repertoire, reflecting heterogeneity in young or aged mice in the recognition repertoire associated with a given antigenic specificity. By preparing F1 anti (parent anti-F1)-suppressor cells directed against CTL from young parental mice (a, b, c), or aged parental mice (x, y, z), we have explored the heterogeneity in the anti-C3H alloreceptor repertoire in individual young or aged C57B1/6 mice. Suppression by immunized F1 animals was assessed in tissue culture (inhibition of mixed lymphocyte culture (MLC) responses) or in vivo (inhibition of lethal GvHD induced by inoculation of parental lymphocytes into sublethally irradiated F1 hybrid mice). Irrespective of the assay system used, the data suggests that the receptor repertoire of aged T lymphocytes uses recognition structures different from those of young individuals, and that there is less individual-to-individual variation in the receptor repertoire of aged mice than in young mice.

Age-related changes in the immune system of mice of eight medium and long-lived strains and hybrids. I. Organ, cellular, and activity changes

Fifty-three organ, cellular and activity indices were assessed in aging mice of 8 strains and hybrids (5 inbred strains, 1 random bred strain and 2 hybrids of inbred strains) in an attempt to determine which aspects of immunologic aging are characteristic of the species. The results indicate that thymic weight, cellular, and activity indices exhibit a statistically significant negative correlation with age for mice of all 8 strains and hybrids; and B cell cellular indices show a statistically significant positive correlation with age for all mice, while the B cell activity index, lipopolysaccharide response, is dependent on the strain or hybrid. This correlation study supports the view that the T cell component of the immune system deteriorates with age while the B cell component remains relatively intact. Further, the results suggest that thymic aging is a characteristic of the mouse species and that the intrinsic "clock" for immunologic aging resides in the thymus, because most splenic and lymph node T cell activity and cellular indices are associated with thymic weight and cellular indices. Finally, the findings that indices which correlate best with age show the same trend for all strains and hybrids examined suggest that (a) if randomly occurring somatic mutation does play a role in immunologic aging, its influence is limited, and (b) genetic factors not easily influenced by environmental factors regulate immunologic aging.

Influence of age on the immunological activity and capacity of the CBA mouse

The immunological activity and capacity were studied in the CBA mouse as a function of its age. The activity was determined by the number of immunoglobulin containing (C-Ig) cells in different lymphoid organs and the immunoglobulin levels of the serum in non-artificially stimulated animals. It was confirmed that in older age the bone marrow takes over from the spleen the role of the major site of immunoglobulin production. A clear decrease in the number of C-Ig cells was observed in the mesenteric lymph nodes and the Peyer's patches. The Ig serum remained constant after the sixth month of age, with the exception of an increase of IgG1 and IgG,2B. There was a striking increase in variation between the individual animals with advancing age. From these data it can be concluded that the B-cell system of old animals is as active as that of young adult animals. The immunological capacity of CBA mice of various ages was assessed by measuring the levels of specific antibodies after the administration of human serum albumin in complete Freund's adjuvant. A severe decline of the primary and the secondary response was observed on ageing. The reaction of three year old animals was negligible. The discrepancy between the declining immunological capacity and the constant or increasing immunological activity is explained by an age-related deficiency of the T-cell compartment in the spleen.

Age-related changes in B and T lymphocytes and decline of humoral immune responsiveness in aged mice

The activity of the immune system declines in an age-related fashion, after reaching a peak in young-adult animals. Although this pattern has been well documented, the mechanisms responsible for the decline of immune potential in senescence have not been fully elucidated. At the same time, it has become apparent that the immune response depends on complex interactions among different cell types. We review the results of the analyses of B- and T-lymphocyte function and activity in the humoral responsiveness of aged mice that have been performed in a number of laboratories, with a variety of experimental techniques. We conclude that an increase in T-cell suppressor function is the first immunologic lesion of aging in mice. This is followed by a decrease in T-cell helper function and finally by a loss of B-cell function.

A multiple-parameter comparison of immunocompetence and tumor resistance in aged BALB/c mice

Several parameters of cell-mediated and humoral immunity were measured in young-adult and aged BALB/c mice and compared with resistance to the ascites form of intraperitoneal induced P815 mastocytoma. It was found that the age-related decline of in vitro phytohemagglutinin (PHA) responsiveness by spleen cells approximated the marked decrease of old mice to tumor-cell challenge and approached that characteristically seen in humoral immunity. Thus, decreased PHA responsiveness of splenic lymphocytes provided as sensitive an estimate of the age-related decline of immunocompetence in old mice as other classical parameters of cell-mediated immunity (e.g. graft-vs-host reaction or in vivo cellular proliferation of parental spleen cells in lethally-irradiated F1 recipients). Results could be interpreted to represent a decreased ability of noncycling T-cells to be released to a functional cycling state.