Analysis on reactivity of human lymphocyte and monocyte-specific antibodies with peripheral blood mononuclear cells from squirrel monkeys (Saimiri sciureus)

Increased Plasmodium falciparum Parasitemia in Non-splenectomized Saimiri sciureus Monkeys Treated with Clodronate Liposomes

A major constraint in the study of Plasmodium falciparum malaria, including vaccine development, lies on the parasite's strict human host specificity and therefore the shortage of animal experimental models able to harbor human plasmodia. The best experimental models are neo-tropical primates of the genus Saimiri and Aotus, but they require splenectomy to reduce innate defenses for achieving high and consistent parasitemias, an important limitation. Clodronate-liposomes (CL) have been successfully used to deplete monocytes/macrophages in several experimental models. We investigated whether a reduction in the numbers of phagocytic cells by CL would improve the development of P. falciparum parasitemia in non-splenectomized Saimiri sciureus monkeys. Depletion of S. sciureus splenocytes after in vitro incubation with CL was quantified using anti-CD14 antibodies and flow cytometry. Non-infected and P. falciparum-infected S. sciureus were injected intravenously twice a week with either CL at either 0.5 or 1 mL (5 mg/mL) or phosphate buffered saline (PBS). Animals were monitored during infection and treated with mefloquine. After treatment and euthanasia, spleen and liver were collected for histological analysis. In vitro CL depleted S. sciureus splenic monocyte/macrophage population in a dose- and time-dependent manner. In vivo, half of P. falciparum-infected S. sciureus treated with CL 0.5 mL, and two-thirds of those treated with CL 1 mL developed high parasitemias requiring mefloquine treatment, whereas all control animals were able to self-control parasitemia without the need for antimalarial treatment. CL-treated infected S. sciureus showed a marked decrease in the degree of splenomegaly despite higher parasitemias, compared to PBS-treated animals. Histological evidence of partial monocyte/macrophage depletion, decreased hemozoin phagocytosis and decreased iron recycling was observed in both the spleen and liver of CL-treated infected S. sciureus. CL is capable of promoting higher parasitemia in P. falciparum-infected S. sciureus, associated with evidence of partial macrophage depletion in the spleen and liver. Macrophage depletion by CL is therefore a practical and viable alternative to surgical splenectomy in this experimental model.

Flow cytometry identification and characterization of mononuclear cell subsets in the neotropical primate Saimiri sciureus (squirrel monkey)

BACKGROUND

The neotropical primate squirrel monkey is used in many areas of biomedical research including neuroendocrinology, immunology and infectious diseases. However, research has been hampered by the lack of immunological tools for this primate.

METHODS

A series of 67 commercially available monoclonal antibodies to human CD antigens or cytokines were tested on Saimiri mononuclear cells and the specificity was assessed by double staining using flow cytometry.

RESULTS

Monoclonal antibodies defining the main mononuclear cells subsets (monocytes, B, T, including CD4 and CD8 T cells) as well as activation markers have been identified. The conditions to specifically identify the various cell subsets using two color flow cytometry and establish their relative proportions have been set-up. We also have established normal values of the main circulating mononuclear cell subsets for adult Saimiri sciureus monkeys from the breeding unit of Institut Pasteur in French Guiana. The distribution between spleen, blood and lymph nodes has been compared.

CONCLUSIONS

These tools allow documenting the phenotype of most Saimiri mononuclear cell subsets and assessing their activation level. This opens new perspectives for vaccinology and immunopathology research in this experimental non-human primate host, in particular for malaria research.