MHC polymorphism in Caribbean African green monkeys.

African green monkeys (AGM) are among the most widely used nonhuman primate models used in various fields of medical research. One species of AGM that originated from West Africa, Chlorocebus sabaeus, was introduced three centuries ago in the Caribbean islands. We present here a systematic study of the major histocompatibility complex (MHC) polymorphism of Caribbean AGM which is currently frequently used as an animal model. We studied 54 animals originated from Barbados (N=25) or Saint Kitts (N=29). The MHC polymorphism was characterized by means of 17 MHC microsatellites spread across MHC and DRB genotyping by DGGE sequencing. We defined nine frequent MHC haplotypes of which two were found in the two insular populations suggesting either past exchanges between the two populations or a common origin of the founders of the two populations. By the analysis of a previously described EST library, we characterized 38 MHC cDNA sequences (17 class I and 21 class II). In conclusion, we characterized for the first time the MHC polymorphism of Barbados and Saint Kitts AGM. We found a restricted polymorphism due to a founding effect, which is responsible for a strong bottleneck. The poorness of MHC polymorphism observed in the Caribbean AGM populations is similar to that observed in the Mauritian cynomolgus macaque population.

Mycophenolic Acid Inhibits p38 Mitogen-Activated Protein Kinase in Human Monocyte-Derived Dendritic Cells Stimulated by Lipopolysaccharide.

Dendritic cell (DC) maturation, a crucial stage in the immune response, can be induced by various stimuli, such as lipopolysaccharide (LPS). Maturation signals trigger up-regulation of costimulatory molecule expression, increasing the ability of DCs to prime T helper cells. We and others have previously reported that mycophenolic acid (MPA) inhibits DC maturation and activation. However, the mechanisms remain unknown. The primary effect of MPA is inhibition of inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in the de novo synthesis of guanosine nucleotide. The process of DC maturation is highly dependent on mitogen-activated protein kinase (MAPK) phosphorylation, especially p38MAPK. We therefore decided to study whether MPA affects these processes. Human monocyte-derived DCs were activated by LPS in the presence or absence of MPA. To assess whether the depletion of guanine affected p38MAPK phosphorylation, increasing doses of exogenous guanosine were added before stimulation. The results by flow cytometry showed that MPA inhibited p38MAPK phosphorylation by 25%. Interestingly, exogenous guanosine did not reverse the MPA inhibition. Our results suggested that MPA inhibits p38MAPK activity independent of IMPDH in human DCs. This effect of MPA may explain its capacity to inhibit maturation marker expression on DCs.

Induction of porcine regulatory cells by mycophenolic Acid-treated dendritic cells.

Tolerance induction in murine allogeneic transplantation is relatively easy, often by induction of regulatory T cells (Treg). Unfortunately, the implementation of these models in clinical situations has not yielded reliable protocols of tolerance induction in humans. Our project sought to create a preclinical model of tolerance induction in large animals. Our current efforts seek to induce and characterize porcine Treg, obtaining dendritic cells (DC) able to preferentially stimulate them. DCs were differentiated from blood monocytes with porcine recombinant interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF) for 6 days. These DCs were then stimulated by human CD40 ligand-transfected L cells with or without mycophenolic acid (MPA) for 48 hours. We analyzed surface marker expression, cytokine synthesis, and ability to stimulate allogeneic peripheral blood mononuclear cells (PBMC). The porcine lymphocytes underwent 4 rounds of 1-week stimulation with allogeneic DC treated or not with MPA. At the end of this coculture we analyzed their capacity to suppress allogeneic PBMC proliferation induced by mature DC. Our results showed that porcine DCs pretreated with MPA display a low expression of B7 costimulatory molecules, produce low levels of IL-12, and induce weak proliferation of allogeneic lymphocytes. Moreover, after 4 rounds of stimulation with MPA-treated DCs, PBMCs were able to inhibit an alloreactive response. These preliminary results suggested induction of a regulatory T-cell population that we are currently seeking to characterize.