A two-site sandwich immunoradiometric assay of squirrel monkey (Saimiri sciureus) IgM using monoclonal antibodies

Effect of valency on binding properties of the antihuman IgM monoclonal antibody 202

A murine monoclonal IgG2a antibody, 202, specific for human IgM, was produced and immunochemically characterized. Binding features of MAb 202, epitope localization, and its accessibility at the quaternary structure of polymeric IgM were investigated. Direct and competitive ELISA with fragments of IgM molecule demonstrated that the epitope recognized by MAb 202 lies on the Fc3 portion of IgM. Sandwich ELISA with MAb 202, which could be used simultaneously to capture and to detect bound IgM, indicated that more than one 202 epitope is present on the IgM molecule. MAb 202 did not precipitate IgM in solution, whereas good precipitation lines were obtained in agarose gel. Binding of MAb 202 to the J chain, C-terminal tailpiece and C mu 2 peptide, which remain attached to the C mu 3 domain of the Fc5 fragment, was excluded by a number of experimental results and structural reasons. Therefore a potential candidate for epitope 202 expression was the C mu 3 domain. MAb 202 did not react with isolated mu chain, which is expected since epitope 202 is of a conformational type. Furthermore, the reaction with monomeric IgM was almost undetectable as was demonstrated by a number of methods (ELISA, immunofluorescence, Western blotting). Since monovalent Fab portions of MAb 202 weakly reacted with polymeric IgM, we concluded that intrinsic affinity of their interaction is low but greatly enhanced by bivalent binding. Antipolymeric IgM binding specificity of MAb 202 was demonstrated only in the case of bivalent binding with a functional affinity constant of Kd = 2.14 x 10(-9) M-1. This implied up to a 10(4) difference between intrinsic and functional affinity, as in the range of concentration used in this study MAb 202 did not react with monomeric IgM.

Immune pressure selects for Plasmodium falciparum parasites presenting distinct red blood cell surface antigens and inducing strain-specific protection in Saimiri sciureus monkeys

The passive transfer of specific antibodies to a naive splenectomized Saimiri sciureus monkey infected with the Palo Alto FUP/SP strain of Plasmodium falciparum resulted in the emergence of parasites resistant to the transferred antibodies. Molecular typing indicated that the original and resistant parasites were isogenic. Saimiri monkeys primed with original parasites were fully susceptible to a challenge by the resistant ones, and vice versa. This absence of crossprotection indicates that strain-specific determinants would be the major targets of protective immunity developed in these monkeys. Phenotypic analysis showed that the surface of the infected red blood cells differed in both lines. Original parasites formed rosettes, autoagglutinated, presented characteristic knobs at the surface of the infected red blood cell, and did not agglutinate in the presence of a pool of human immune sera. In contrast, the resistant parasites did not form rosettes, did not spontaneously autoagglutinate, presented abnormal flattened knobs, and formed large aggregates in the presence of a pool of human immune sera. The presence of strain-specific determinants at the surface of the resistant parasites was confirmed by surface immunofluorescence and agglutination using homologous Saimiri serum. Neither the original nor the resistant parasites cytoadhered to an amelanotic melanoma cell line, suggesting that cytoadherence and agglutination can be dissociated. These results indicate that parasites that differ by the antigens exposed at the surface of the red blood cell induce strain-specific immunity. Furthermore they show that rosetting and nonrosetting parasites differ in their antigenic properties and do not crossprotect.

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.