Complement Receptor Lymphocytes in the Rabbit

Abstract

Abstract Complement receptor lymphocytes (CRL) were detected in various rabbit lymphoid tissues by the ability of these CRL to form rosettes with sheep red blood cells coated sequentially with rabbit antiserum directed against sheep red blood cell stroma and horse serum as a nonhemolytic source of complement (EAC). The rosette assay was shown to be specific for complement receptor (CR) activity and the EAC capable of detecting both C3b and C3d specific receptors. With lymphocyte preparations containing less than 5% phagocytic cells, the average per cent CRL in the various tissues studied was as follows: thymus 1%, popliteal lymph node 18%, spleen 30%, appendix 35%, and peripheral blood 45%, Double assays in which the lymphocytes were prestained with an FITC-labeled Fab′ fragment of a goat anti-rabbit Fab antibody before rosetting indicated that CRL were a subpopulation of surface immunoglobulin (SIg)-bearing lymphocytes in popliteal lymph node, spleen, and peripheral blood. In the appendix, however, in addition to finding SIg+ CR+ and SIg+ CR- populations, an SIg- CR+ population was consistently found. Double assays employing FITC-labeled goat antibodies specific for µ, α, and γ determinants were also performed to determine if there was any relationship between the class of Ig displayed and presence of CR. It appeared that an approximately equivalent percentage of both IgM- and IgG-bearing cells also displayed CR. Experiments in which appendix cells were treated with Pronase to remove SIg and CR and the cells cultured in vitro to allow regeneration of surface markers confirmed the existence of SIg+ CR+, SIg+ CR-, and SIg- CR+ lymphocyte subpopulations. Whether the SIg- CR+, population represents a developing B cell population which will eventually also express SIg or whether it belongs to the T or “null” cell populations is unclear at present.