The Journal of Immunology, Vol 141, Issue 2 620-626, Copyright © 1988 by American Association of Immunologists

ARTICLES

Independent regulation of B cell responses to surface and subsurface epitopes of African trypanosome variable surface glycoproteins

DM Reinitz and JM Mansfield
Veterinary Science Department, University of Wisconsin, Madison 53706.

Regulation of B cell responses to the trypanosome surface Ag was examined in H-2k compatible "responder" B10.BR and "nonresponder" C3H mice after infection with two variant clones of Trypanosoma brucei rhodesiense. Development of a selective RIA for independent detection of antibody binding to surface (exposed) and subsurface (buried) epitopes of the trypanosome variable surface glycoprotein (VSG) molecule permitted sensitive quantitation and kinetic characterization of immune responses to these epitopes. The infected B10.BR mice responded to both exposed and buried VSG epitopes of clone LouTat 1 trypanosomes, whereas a B cell response by C3H mice to exposed VSG epitopes was not detected by RIA analyses at any time. However, VSG- specific IgM and IgG responses were produced to buried VSG epitopes, demonstrating that LouTat 1 induced immunoregulation was specific only for the B cell responses to exposed VSG epitopes. Subsequently, comparisons of B10.BR and C3H B cell responses to a heterologous variant, LouTat 1.5, were made. The results revealed that both infected mouse strains produced VSG 1.5-specific antibody to exposed and buried epitopes with different kinetics and maximal sera concentrations, showing, therefore, that these responses are not coordinately regulated. In addition, it was clear that the observed immunosuppression to exposed LouTat 1 VSG epitopes in C3H mice could be regulated by the parasite since functional C3H B cell responses were mounted against exposed VSG epitopes of a closely related variant (LouTat 1.5) after infection.

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