Fc receptors on rabbit lymphocytes. Identification and organ distribution of rosette‐forming cells; cocapping with surface immunoglobulin

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Abstract
Fc receptor (FcR)-bearing cells were demonstrated using ox erythrocytes coated with homologous IgG-type antibodies (EAY) in rabbit peripheral blood leukocytes (PBL) and in various lymphoid organs. Discrimination of the rosette-forming cells (RFC) is carried out after prior ingestion of tetramethylrhodamine isothiocyanate-labeled latex particles and in transmission electron microscopic studies. Most of the nonlymphoid cells (5-10%) in PBL and spleen cell suspensions expose FcR. These nonlymphoid cells are almost absent in other lymphoid organs, except in bone marrow. The average percentage of cells rosetting with IgG-sensitized erythrocytes (EAγRFC) in lymphoid cell preparations of the various tissues was as follows: PBL 25%, bone marrow 65%, appendix 37%, spleen 40%, Peyer's patches 44%, thymus 2% and peripheral lymph node 27%. The nature of FcR-bearing PBL was further studied using F(ab′)2 anti-IgM, anti-IgA or anti-T cell conjugates. About half of the population of B cells, bearing IgM or IgA, express FcR. Moreover, about 80% of the RFC are found within the B cell population. Only a few T cells were found rosetting with EAγ suggesting that most of the non-B lymphoid RFC are “null” cells. In different lymphoid organs, the percentages of EAγRFC and B cells are comparable but not identical. A greater part of the EAγRFC also expresses the receptor for the third component of complement. After capping of membrane IgM determinants, FcR is located in the same cap on the majority (60%) of the FcR-positive IgM-capped cells.