Lymphocyte Subsets in the Young and Aging Marmoset (Callithrix jacchus)

The aging common marmoset's immune system: From junior to senior

The social, health, and economic challenges of a steadily increasing aging population demand the use of appropriate translational animal models to address questions like healthy aging, vaccination strategies, or potential interventions during the aging process. Due to their genetic proximity to humans, especially nonhuman primates (NHPs) with a relatively short generation period compared to humans, qualify as excellent animal models for these purposes. The use of common marmosets (Callithrix jacchus) in gerontology research steadily increased over the last decades, yet important information about their aging parameters are still missing. We therefore aimed to characterize their aging immune system by comprehensive flow cytometric phenotyping of blood immune cells from juvenile, adult, aging, and geriatric animals. Aged and geriatric animals displayed clear signs of immunosenescence. A decline in CD4/CD8 ratio, increased expression of HLA-DR and PD-1, higher frequencies of CD95⁺ memory cells, alterations in cytokine secretion, and a decline in the proliferative capacity proved T cell senescence in aging marmosets. Also, the B cell compartment was affected by age-related changes: while overall B cell numbers remained stable with advancing age, expression of the activation marker CD80 increased and immunoglobulin M expression decreased. Interestingly, marmoset B cell memory subset distribution rather mirrored the human situation than that of other NHP. CD21⁺ CD27^- naïve B cell frequencies decreased while those of CD21^- CD27^- tissue memory B cells increased with age. Furthermore, frequencies and numbers of NK cells as part of the innate immune system declined with advancing age. Thus, the observed immunological changes in common marmosets over their life span revealed several similarities to age-related changes in humans and encourages further studies to strengthen the common marmoset as a potential aging model.

Effect of neonatal treatment with a gonadotropin releasing hormone antagonist on developmental changes in circulating lymphocyte subsets: a longitudinal study in male rhesus monkeys

We have examined changes in circulating lymphocyte subsets from the neonatal period until adulthood (4 months until 5.5 years of age) in male rhesus monkeys, and the impact of neonatal treatment with a GnRH antagonist (Ant) or Ant and androgen (Ant/And) on these parameters. Absolute numbers of lymphocytes, B cells, total T lymphocytes, and CD4+ T cells decreased, neutrophils increased, and CD8+ T cells did not change with age. WBC counts increased between 4 mo and 2 years of age and then fell to neonatal levels over the next two years. The decline of CD4 + T cells in association with stable CD8+ T cell levels resulted in an age-related decrease in the CD4+/CD8+ T cell ratio. At 4 months of age, WBC's, lymphocytes, total T cells, CD8+ T cells and B cells were lower in Ant- and Ant/And-treated animals compared to controls. With the exception of WBC counts, these values had normalized by 2 years of age. Reduced WBC levels in treated animals persisted through adulthood. CD4+ T cell levels tended to be lower in Ant-treated and higher in Ant/And-treated animals than in controls at 4 months of age. CD4+ T cells remained lower in Ant- than in Ant/And-treated animals at most ages. The higher CD4 + T cell counts in Ant/And-treated animals resulted in an elevated CD4 + /CD8 + T cell ratio that persisted until the onset of year 5. During years 5 and 6, seasonal fluctuations in WBC's and neutrophils were observed with counts being higher in the breeding (fall) than in the nonbreeding (summer) season. The data document that developmental changes in circulating immune cells in the rhesus monkey are qualitatively similar to those reported in humans, and provide further evidence that neonatal treatment of male rhesus monkeys with Ant or Ant/And may alter early programming of the immune system.

Changes in lymphoid tissue after treatment with a gonadotropin releasing hormone antagonist in the neonatal marmoset (Callithrix jacchus)

PROBLEM

The effect of neonatal treatment with a gonadotropin releasing hormone (GnRH) antagonist on the morphology and distribution of lymphocytes in lymphoid tissue of the infant marmoset was examined.

METHOD OF STUDY

From a screened panel of antihuman antibodies for specific immune cells, antibodies for the CD20 and CD3 antigens showed excellent reactivity with marmoset tissue. Five sets of marmoset twins were treated with either the GnRH antagonist or a vehicle from birth, and were euthanized at 7 to 9 (3 sets) or 16 to 20 weeks (2 sets) of age. The spleen, thymus, and inguinal lymph nodes from each animal were processed for immunocytochemistry, and the number of cells expressing the CD20 and CD3 antigens were quantified.

RESULTS

Control twins exhibited high plasma levels of testosterone, characteristic of the neonatal period, whereas testosterone concentrations were reduced (P = 0.001) to detection limits in the GnRH antagonist-treated twins. Microscopic evaluation suggested that treatment reduced the volume and cellularity of the thymic cortex, resulting in a decrease in the cortical-to-medullary ratio. Treatment reduced (P = 0.046) the number of thymocytes expressing the B-cell antigen (CD20) and marginally lowered (P = 0.067) the number expressing the T-cell antigen (CD3) in the thymic medulla. In the spleens of treated animals, periarterial lymphatic sheaths were less prominent on microscopic examination, and there were marginally fewer (P = 0.064) CD3+ cells. Numbers of CD20+ lymphocytes in the peripheral white pulp of the spleen and in the germinal centers of the lymph nodes, or CD3+ cells in the paracortex and germinal centers of the lymph nodes, were not altered by treatment.

CONCLUSION

Neonatal treatment with a GnRH antagonist may alter maturational processes for B and T cells in the thymus and spleen of the marmoset and may deprive the immune system of its normal sensitivity to GnRH at a potentially critical time in development.

Comparative study on age-dependent development of surface receptors on peripheral blood lymphocytes in children and young nonhuman primates (marmosets)

General conformity was found concerning age-dependent changes in the major subsets (CD4, CD8, CD2, CD20) and the adhesion molecules CD11a and CD29 on peripheral blood lymphocytes in children and young marmosets (Callithrix jacchus). Differences exist in the expression of the surface receptors CD45RA and CD56. Taking the total number of white blood cells into account, an age-related increase in the absolute numbers of peripheral blood lymphocytes was found in marmosets whereas in children, an age-dependent decrease was observed. The definition of reference ranges for different stages of maturation in children and young marmosets may serve as a basis on which comparative risk assessment of possible effects on lymphocyte subsets after pre- or perinatal drug exposure can be estimated.

Manipulating blood T cells and B cells from squirrel monkeys: some technical considerations

The squirrel monkey Saimiri sciureus is an experimental host for a range of human pathogens, and for the assessment of vaccine candidate antigens and vaccine strategies. This experimental host is thus particularly suitable for the follow-up of humoral responses. To understand some of the mechanisms that underlie the defense against experimental pathogens, there is a need of basic knowledge on cellular immune effectors also. The authors report here their experience in characterizing squirrel monkey blood T and B lymphocytes, and in studying in vitro induced activation and proliferation of T and B cells. Particular emphasis is given to the in vitro differentiation of squirrel monkey B cells into immunoglobulin secreting cells, with respect to Plasmodium falciparum antigens.

Peripheral blood mononuclear cells in the squirrel monkey Saimiri sciureus: characterization and functional aspects of T lymphocytes

Characterization and functional aspects of squirrel monkey peripheral blood mononuclear cells (PBMC), and mainly T cells, are described in the present paper; this should enable the study of cellular immune responses in an experimental model for malaria. PBMC were obtained from Ficoll-Hypaque gradient separation and fractionated into T cells and non-T cells by means of E-rosetting techniques and adherence to plastic dishes. PBMC subset phenotypes were characterized by means of monoclonal antibodies (mAb) directed against human leukocyte differentiation antigens (Ag), fluoresceinated lectins, anti-surface Ig (squirrel-monkey-specific) antibodies (Ab) and latex bead ingestion assays. PBMC functions were assayed through lymphoblastic transformation tests (LTT) in the presence of either numerous mitogenic, comitogenic and anti-mitogenic lectins or anti-human leukocyte differentiation Ag mAb. We sought to standardize reference values for lymphocyte phenotypes and functions in normal squirrel monkeys (prior to experimental infection). We also present evidence that splenectomy (generally rendered necessary for experimental human malaria infection) performed six months prior to the present investigation did not modify PBMC numbers and functions in the tested animals.

Analysis of T lymphocyte subsets in tamarins with colitis and colon cancer

The cotton-top tamarin, Saguinus oedipus, serves as an animal model for the study of human colon cancer. This New World monkey has a high incidence of colitis and colon cancer that develops spontaneously. Evidence suggests that these diseases may be the result of a virally induced immunodeficiency. We have shown that T4+/T8+ cell ratios are significantly altered in tamarins with acute colitis and colon cancers. The T4+/T8+ ratios were 1.50 +/- 0.09, 0.70 +/- 0.05, and 0.48 +/- 0.05 for negative controls, acute colitis, and cancer positive tamarins, respectively. Statistical analysis showed a significant difference (p less than or equal to .0005) between negative controls vs. acute colitis and cancer positive groups.