Usha Ponnappan

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-Dependent Changes in Isotype Expression and Down-Regulation of C57BL/6 Mice

Age‐related changes in antibody response and tolerance inducibility are polymorphic; in this paper isotype changes in ageing C57BL/6 mice are examined Female C57BL/6 mice of various ages were immunized with either heat‐aggregated RGG (a‐RGG) or phosphorylcholine conjugate of RGG (PC‐RGG); other animals of the same ages were given aggregate free RGG, followed by injections with either aggregated RGG or haptenated RGG. Sera from these four groups were analysed for antibody isotype. The data presented here indicate that age‐related changes in isotype predominance and magnitude are different for different determinants. The capacity to be down‐regulated appeared to undergo different age‐related changes with different isotypes: there is split tolerance in isotypes. Age‐dependent changes in T‐ and B‐cell tolerance could be deduced by comparing responses of animals to hapten and to carrier determinants. In 5‐week‐old animals tolerance to hapten was more profound than tolerance to carrier. It was concluded that T‐cell regulation dominated the response at this age. With advancing age, i.e. by 95 weeks, tolerance is observed in response to hapten but not in response to carrier determinants. We concluded that suppressor cells were induced by aggregate free RGG and affected the response of ‘naive’ but not of ‘experienced’ B cells.

Isotype-specific resistance against tolerance induction in SJL mice

Age-related changes in antibody response of SJL mice were examined in terms of isotype expression after treatment with immunogen or with immunogen, preceded by the molecule in normally tolerogenic form. We report here that tolerance induction and resistance to down regulation are isotype specific. Tolerance can be induced in terms of all detectable isotypes at the age of 5 weeks. In older SJL mice, tolerance to the carrier is found in IgM antibody, whereas there is resistance against down regulation in terms of IgG2a and IgG2b isotypes, and sensitization in terms of IgG3, IgG1, and IgA antibody. Furthermore, the degree of down regulation is determinant dependent. This was observed when older SJL mice, pretreated with the carrier in a normally tolerogenic form, were immunized with haptenated carrier and tested for their response to hapten and carrier determinants. In this case, IgA antibody shows tolerance to the hapten and sensitization by carrier determinants.

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.

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.

Age-dependent changes of isotype and idiotype expression in the antibody response to the phosphorylcholine hapten in BALB/c mice.

The distribution of antibodies among different isotypes in an immune response to a given antigen reflects the immunoregulatory linkage of T and B cell compartments, the genetic background of an individual and the functional state of its immune system. In addition, idiotypes are markers for the clonal origin of antibodies and their genetic relationship. Therefore, we have analyzed the isotype patterns and development of the major idiotype (T15) in BALB/c mice of different ages, immunized with a T-cell-dependent phosphorylcholine conjugate. The response was dominated by mu, gamma 3 and gamma 1 isotypes. The proportion of these antibodies changed in the progress of immunization but not with age in the primary response. An age-dependent change of the isotype distribution was observed only in the memory response. The T15 idiotype was dominantly expressed in the primary response and decreased in the memory response by 80-95% independently of the age of the mice. The results demonstrate that 2 populations of anti-phosphorylcholine antibodies which both prefer particular isotypes are expressed according to the functional state of the T and B cell compartments with age.

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 isotype 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 CS7BL/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.

Fine Specificity and Isotype Expression of Anti‐PC Antibodies in BALB/c, MRL/Mp‐1pr/1pr, and −+/+ Mice at Different Ages

The MRL/Mp congenic mouse strains develop autoimmune disease with age. We have investigated age‐ and autoimmune‐related changes in fine specificity, isotype spectra and T15 idiotype expression of the anti‐phosphorylcholine (PC) response in BALB/c, MRL/Mp −+ and ‐lpr congenic mice and in (BALB/c x MRL/Mp‐lpr) F1 hybrids. Two groups of anti‐PC antibodies with distinct fine specificity are elicited in the memory response. Group I antibodies recognize the PC moiety and express the T15 idiotype. Antibodies of group II are specific for phenyl‐phosphorylcholine and are found predominantly in the memory response. In the MRL/Mp‐lpr and −+ strains only a minor population of antibodies expresses the T15 idiotype at all ages. However, a third group of antibodies was observed which binds to PC‐coated proteins and to Diplococcus pneumoniae R‐36A. This binding was not inibited by PC‐chloride and appeared mainly in the memory response at old age. The isotype distribution among anti‐PC antibodies was similar in all strains analysed. In the initial response primarily μ, γ3 and γ1 isotypes were produced, while in the memory response γ1 was dominant.

Immunosuppression after injection of friend virus into C57BL/6 mice of different ages

Injection with Friend virus (FV) causes immunosuppression in young and old C57BL/6 mice, i.e. it occurs whether or not the virus replicates very briefly or for a long period. There are only minor age-related differences in the extent of immunosuppression, except that suppression appears to persist somewhat longer in old than in young animals.