Immune reactivity during aging. I. T-helper dependent and independent antibody responses to different antigens, in vivo and in vitro

The unresponsiveness of aged mice to polysaccharide antigens is a result of a defect in macrophage function

A reduction in macrophage (MPhi) function with aging makes mice less responsive to bacterial capsular polysaccharides, such as those present in the pneumococcal polysaccharide vaccine, a model of thymus independent (TI) antigen (Ag). Using trinitrophenol (TNP)-lipopolysaccharide (LPS) and TNP-Ficoll, two other well-studied TI Ag, we studied the mechanistic basis of reduced MPhi function in the aged. We show that aged mice are profoundly hyporesponsive to these TI Ag. As a result of a requirement for MPhi, highly purified B cells from young-adult mice do not respond to TI Ag. When purified, young B cells were immunized with TNP-Ficoll, the antibody production from those cultures reconstituted with MPhi from aged mice was significantly lower than that seen with young MPhi. Consequently, this unresponsiveness can be overcome by a mixture of interleukin (IL)-1beta and IL-6. Upon stimulation with LPS, in comparison with young MPhi, aged MPhi secreted reduced amounts of IL-6, tumor necrosis factor alpha, IL-1beta, and IL-12, cytokines necessary for B cells to respond to TI Ag. LPS also induced aged MPhi to produce an excess of IL-10. Neutralization of IL-10 enhanced the production of proinflamatory cytokines by MPhi upon LPS stimulation and also induced Ab production by aged splenocytes. Thus, the inability of aged MPhi to help the B cell response appears to be caused by an excess of IL-10. As aged MPhi have a reduced number of cells expressing Toll-like receptor 4 and CD14, the imbalance in cytokine production might be partly a result of fewer cells expressing key components of the LPS receptor complex.

Biogerontology research in Israel

The article describes the special features of gerontology research that has been expanding for five decades in Israel, and outlines the research in the biology of aging, covering a wide spectrum of areas and topics. A variety of associations, institutes and centers that have been established over the years play an important role in furthering the research and academic training.

The influence of aging on the induction and manifestations of experimental systemic lupus erythematosus

The influence of age on autoimmunity was studied in a model in which experimental systemic lupus erythematosus (SLE) is induced in normal mice by the injection of a human monoclonal anti-DNA antibody expressing a common idiotype designated 16/6 Id. The resulting disease is expressed by the production of a variety of autoantibodies and clinical manifestations characteristic to human SLE. Female BALB/c mice, at ages of 2 and 12 months, were immunized with the 16/6 Id. Mice were tested periodically for the presence of autoantibodies. The production of all autoantibodies tested was significantly lower in the older mice as compared to the group of young mice. Clinical manifestations which included leukopenia, increased erythrocyte sedimentation rate and proteinuria were similar in both age groups. Kidney evaluations revealed differences among the two groups of mice. While in all kidney sections of young mice multiple immune complex deposits were detected, in the group of older mice half had similar pathology while the rest either were negative or had only segmental and partial glomerular immune complex depositions. Thus, aging is associated with a decrease in the capacity to respond to the pathogenic anti-DNA, 16/6 Id, by the production of antibodies and autoantibodies and in the expression of a milder disease.

Effects of aging on the induction of experimental systemic lupus erythematosus (SLE) in mice

The study was designed to determine whether manifestations of autoimmunity are altered with age, using an experimental model in which systemic lupus erythematosus (SLE) is induced in mice. Young (2-month-old), and aging (18-month-old) BALB/c female mice were immunized with a human monoclonal anti-DNA antibody that bears a common idiotype (16/6 Id). Control groups were either left untreated or were injected with human IgM (HIgM). Anti-16/6 Id levels were found to be significantly lower in the old mice than in the young. Similarly, anti-anti-16/6 Id (murine 16/6 Id+) values were lower in the old. Mice injected with the 16/6 Id also produced various autoantibodies, including anti-dsDNA, anti-RNP, anti-Sm and anti-histones antibodies. The levels of these antibodies were lower in the old mice than in the young, yet the differences were not statistically significant. Levels of autoantibodies examined in control animals were either similar in both age groups (anti-RNP and histones) or lower in the old (anti-dsDNA and Sm). Four months after a booster injection of 16/6 Id, the young mice developed clinical manifestations of SLE, including proteinuria and leukopenia, which were seen, in milder form, in the aged mice. Immune complex depositions examined by immunohistology on kidney sections suggested similar differences based on the age of the animals. Our results suggest that aging might actually be associated with a decline in the capacity to produce autoimmune responses.

Phenotypic and functional properties of B lymphocytes from aged mice

Phenotypic and functional properties of B lymphocytes from individual young and old mice of different inbred strains were studied. B lymphocyte subpopulations defined by the ratios of the densities of cell surface IgM and IgD were found to be altered with age. However, such alterations in B cell subsets were found only in 30-40% of the old mice. B cell mitogenic responses to anti-mu and anti-Lyb2 antibodies were decreased in a majority of DBA/2 mice. Proliferative responses to LPS and anti-mu were reduced only in a minority of CBA/Ca mice but there was a very good correlation in the responsiveness of the old mice to LPS and anti-mu. The anomalous properties of the individual old mice of these inbred strains may be due to a heterogeneity in the effects of aging or due to environmental influences.

A specific defect in the proliferative capacity of B cells from old mice stimulated with autoreactive T cells

B lymphocytes from aged mice were found to be defective in their ability to proliferate in response to stimulation with an autoreactive T cell clone D1.4. The differentiative response leading to antibody secretion was also impaired in the auto D1.4 T cell-stimulated B cells from old mice in comparison to similarly stimulated B cells from young mice. The B cells from old mice were competent in activating the autoreactive T cells such that the T cells were induced to proliferate. The B cell defect appears to be restricted to a certain phase of B cell activation, since old mouse B cells responded to the auto D1.4 T cells by increasing cell surface Ia as well as size, but failed to incorporate tritiated thymidine. The responsiveness to interleukin-4 was found to be similar between B cells from young and old mice. It appeared that the B cells from old mice are specifically defective in progressing from the G0 phase of cell cycle into the S phase when stimulated with the auto D1.4 T cells.

Enhancement of the response of ageing mouse lymphocytes by in vitro treatment with lecithin

The effect of treatment with phosphatidylcholine (lecithin) has been examined on splenocytes from young (6 months) and aged (greater than 20 months) (C3H/eB X C57BL/6)F1 male mice, by probing their responsiveness to proliferative signals of mitogens and mixed lymphocyte reaction. This study was initiated since old mice have been known to manifest an increased ratio of cholesterol: phospholipids (C/PL) in their plasma membranes. Unlike the case in young mice, enhancement in proliferative responses was demonstrated on cells from the old after incubation with lecithin. This enhancement was achieved using a variety of methods by which lymphocytes were exposed to the lipids, and which were all designed to reduce the C/PL ratio in the plasma membrane. The observed differences in response to lecithin treatment between young and old did not stem from different extents of lipid incorporation, and seems unlikely to be a result of modified binding of the mitogens after treatment with the lipid. The data suggest that the normal functional performance of specific reactions, which decline with age, may be restored artificially at an appropriate age, if other complementary functions have not been damaged.

Changes in the prolactin-binding capacity of mouse hepatic membranes with development and aging

The objective of this study was to document the developmental changes in the prolactin-binding capacity of hepatic membranes of the female mouse. Prolactin-binding capacity was measured in the microsomal membranes of liver obtained from C3H female mice at various ages. Binding capacity of these membranes remained low until 21 days of age after which it increased and reached the adult levels by 44 days of age. Additional studies were made to observe this parameter in male and female mice during aging. Both female and male mice at 450-470 days of age had values of prolactin binding that were 66% and 79% that of the 77-day-old animals, respectively. A significant increase in membrane lipid microviscosity was observed in animals from both sexes at 450-470 days of age. This was in agreement with earlier studies that showed that prolactin receptors of hepatic membranes are modulated by changes in the membrane lipid microviscosity. These changes suggest that such modifications of cellular membranes are interrelated and that changes in the membrane microviscosity with aging may be a factor modulating cellular responses in older animals.

Antigen responsiveness of the mature and generative B cell populations of aged mice

The deficit of humoral immune responsiveness associated with aging was investigated at the level of individual antigen-specific B cells. It was found that mature dinitrophenyl (DNP)-responsive B cells isolated from the spleen of aged mice gave rise to clones of antibody-forming cells that were normal with respect to both the amount and relative affinity of anti-DNP antibody produced. However, although the proportion of immunoglobulin-bearing cells in the spleen of aged mice was normal, the proportion of cells that responded to T cell dependent DNP-specific stimulation (1.1 per 10(6) injected cells) was significantly lower than the proportion that responded when cells were obtained from the spleen of young mice (2.3 per 10(6) injected cells). To examine the origin of this diminution in antigen-responsive B cells, the responsiveness of precursor cells from the B cell generative pool isolated as the surface immunoglobulin negative (sIg-) cells within the bone marrow was evaluated. The frequency of DNP-responsive cells in both intact bone marrow cell suspensions and the sIg- subpopulation was not significantly different when such cells were isolated from aged vs. young individuals. Thus, it would appear that among the immunologic deficits associated with aging is a decrease in the proportion of antigen-responsive B cells, which is associated with maturation of B cell clones in the aged environment and occurs during the migration of cells from the bone marrow to the spleen.

Bacteria-immune system interactions. XII. Effects of aging on Balb/c mice responsiveness to Salmonella typhimurium

Age-associated changes in reactivity to bacteria were tested at several levels. At the level of bacteria binding to lymphocytes, there were no significant differences between young and old mice, however the lymphocytes from adults bound less bacteria than the other age groups. Similarly, the lymphocytes from spleens of adult mice were less efficient in killing bacteria than all the other age groups. The lymphocytes of young mice had higher and longer range reactivity than the ones from old mice. Bacterial stimulation did not produce significant levels of thymidine incorporation in any of the age groups tested.

Immunoregulation in senescence: increased inducibility of antigen-specific suppressor T cells and loss of cell sensitivity to immunosuppression in aging mice

Azobenzenearsonate (ABA)-specific T cell-mediated suppression has been studied in aging mice. ABA-specific suppressor T cells were induced in young and old mice by injection of ABA conjugated to syngeneic spleen cells (ABA-SC). These suppressor cells were tested for their ability to suppress the in vitro anti-trinitrophenyl (TNP) antibody response of lymph node cells obtained from ABA-keyhole limpet hemocyanin (KLH)-primed young or old mice and cultured with TNP-ABA-KLH. Suppressor T cells were found to be more easily induced in old than in young mice but to suppress less efficiently the antibody response of cells from old than from young mice. The increased inducibility of antigen-specific suppressor T cells in old mice is compatible with the age-dependent decline of immune responsiveness to exogenous antigens. The loss of cell sensitivity to antigen-specific immunosuppression as well as the lack of evidence for increased nonspecific suppression in old mice is consistent with the age-related increase in autoimmune disorders. These findings provide a unifying explanation for the most relevant immunological phenomena of senescence.

Developmental aspects of T-suppressor cells induced by hapten-carrier conjugates

The capacity of newborn liver and of aging mouse spleen to give rise to suppressor cells interfering specifically with an anti-hapten antibody response was investigated. The experimental system to induce suppressor cells was used on sequential treatment with a hapten (DNP or NIP) coupled to two different carrier molecules (i.e., DNP-RSA and DNP-BGG, respectively). Suppressor cells developing under such conditions are Thy 1.2+, nylon wool effluent, PNA+, I-J+ cells. Newborn liver cells were found to be capable of differentiating into such suppressors. Aging mouse spleen cells did not manifest such specific suppression, yet they did interfere with the antibody response in a nonspecific manner.

Immune reactivity during aging. II. Analysis of the cellular mechanisms involved in the deficient antibody response in old mice

Analysis was made of the cellular basis of decline in the antibody immune response with advancing age. Employing the cell transfer system, it was found that spleen cells of aged mice have a limited capacity to react to SRBC when transferred into young irradiated recipients. Partial reconstitution was achieved when thymus cells from young untreated donors were applied together with the spleen cells, suggesting that deficiency in T helper cell function is responsible in part for the limited response. Similar studies using the T helper-independent antigen PVP also resulted in low levels of antibodies in the irradiated recipients. Treatment of the spleen cells with anti-theta serum before transfer did not lead to an increased response. Hence, it is suggested that the reduced response is related to limited function in the B cell compartment, and not to function of T suppressor cells. Transfer of bone marrow cells from aged into young irradiated recipients indicated that cells capable of differentiation into antibody-producing cells are available during aging. It is thus maintained that the defect at the B cell level is of a developmental nature.