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

Abstract

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.

Differential Activities of Rabbit Bone Marrow Suppressor Cells

“…The high levels of proliferation induced among BM cell populations by IC were ac companied by increased proportions of FcyR+ cells. Since 80% of rabbit FcyR+ lymphocytes have been re ported to be B cells [15], the preferential induction of FcyR+ cells by 1C was consistent with the findings of Morgan and Weigle [10], who reported that IC in duced B cell proliferation and polyclonal activation.…”

“…Such increase in FcyR expression may have been necessary before these cells could respond to IC [10]. If B cells were the targets of IC stimulation [10], then FcyR+ cell suppression must have acted on an early stage of differentiation because B cells [15] and pre-B cells [16] would have been removed by the rosetting techniques. The inability of FcyR+ suppressor cells to block stimulation with IC might have been due to the preferential induction by IC of IgG responses [8], since BM suppressor cells have been reported to block IgM, but not IgG responses [1].…”

Surface Ig on rabbit lymphocytes Rabbit B and T cells are distinct populations

“…(c) Whole blood was mixed with Earle's 1% BSA medium, layered on Ficoll-Hypaque (e 1.077) and centrifuged for 30 min at 1000 x g as described by B~y u m [15]. Cell suspensions from lymphoid organs were prepared by pushing minced tissues through nylon gauze and washing the cells in cold medium [13].…”

“…The F(ab'h y components of anti-Ig antisera were prepared by pepsin digestion followed by filtration over Sephadex G-150 and a Staphylococcal Protein A-Sepharose 4 B column (Pharmacia, Uppsala, Sweden) to remove residual Fc and undigested IgG. Conjugation with fluorescein isothiocyanate (FITC) or tetramethylrhodamine isiothiocyanate (TRITC) was performed as will be described [13] and gave rise to conjugates with molar fluorochrome/protein ratios of 1.8-4.5. All conjugates were centrifuged (30 min, 10000 x g), filtered through 0.45 p Millipore membranes and stored in 20 ml aliquots at -20°C.…”