Persistence of anti-immunoglobulin on the lymphocyte surface

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

Fc receptor (FcR)-bearing cells were demonstrated using ox erythrocytes coated with homologous IgG-type antibodies (EA gamma) 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 (EA gamma RFC) 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 EA gamma suggesting that most of the non-B lymphoid RFC are "null" cells. In different lymphoid organs, the percentages of EA gamma RFC and B cells are comparable but not identical A greater part of the EA gamma RFC 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.

Allelic exclusion in the B lineage cells of the rabbit

Allelic exclusion of the K polypeptide chain allotypes b4 and b5 of the rabbit exists for the immunoglobulins of almost all plasma cells and of most mature small B lymphocytes. However, both these alleles are expressed simultaneously in rare plasma cells and in an usually large fraction of the lymphoid cells of the bone marrow. Our experiments support the idea that such bone marrow B lineage cells do not always show allelic exclusion.