Cells and mediators which participate in immunoglobulin synthesis by human mononuclear cells. II. The mechanism of null cell participation in immunoglobulin synthesis and secretion by B cells

Abstract

SUMMARYImmunoglobulins were synthesized and secreted by human B cells cultured with T cells with receptors for FcM (TM) helper cells, monocytes, null cells and PWM for 7 days. Immunoglobulin synthesis did not take place if the null cells were omitted from the cultures irrespective ofthe duration ofthe culture period. Null cells incorporated into the cultures at only 25% of their optimal concentration did not affect immunoglobulin synthesis markedly by the cultured B cells. However, the number of B cells in the culture could not be diluted without an accompanying marked reduction in immunoglobulin synthesis. The B cells synthesized and secreted significant quantities of immunoglobulin even when the null cells were added as late as day 6 ofthe 7-day culture whereas no or very little immunoglobulin was synthesized if the B cells were not present from the beginning of the 7-day culture. It was demonstrated that cultured null cells do not transform into B cells and do not attain their immunoglobulin-synthesizing function. Furthermore, cultured B cells do not transform into null cells and do not attain their helper function. The null cells can also be distinguished from the B cells on the basis of cell-surface markers, receptors, and blastogenic responsiveness to phytomitogens. It is concluded that (i) the human circulating B cells require the null cells, in addition to the TM cells, monocytes and PWM, in culture in order to synthesize and secrete immunoglobulin; (ii) the null cell signal that stimulates immunoglobulin synthesis and secretion by the B cells is probably the last signal following the T^ helper cell, monocyte and PWM signals received by the B cells; and (iii) the null cells and the B cells constitute distinct lineages of cells.

Cells and mediators which participate in immunoglobulin synthesis by human mononuclear cells. III. Null cells secrete a factor(s) (human immunoglobulin synthesis/secretion-facilitating factor) that can replace the null cells in the synthesis of immunoglobulin by cultured B cells

“…In previous investigations (Richter & Jodouin, 1985;Richter et al, 1990) it was demonstrated that the null lymphocytes are obligatory participants in immunoglobulin synthesis by cultured B cells, as are the TM helper cells, monocytes and PWM. However, the mechanism of null cell participation was not determined.…”

“…The methods used for the isolation of the MNC from whole blood of healthy volunteers, the fractionation ofthe MNC into T and non-T cells by rosetting with sheep erythrocytes, the formation ofthe EAG indicator cells, the separation ofthe non-T cells into the null cells and the B cells by rosetting the non-T cells with EAG, the isolation of the TM helper cells, the elimination of monocytes by carbonyl iron phagocytosis, the immunofluorescent assay to detect immunoglobulin-synthesizing cells, and the ELISA to determine IgG and IgM secreted by the cultured cells, have all been described in previous publications (Richter & Jodouin, 1985;Richter et al, 1990).…”

“…It was demonstrated that the null cells are distinct from the B cells in terms of surface markers and receptors, in their blastogenic responses to phytomitogens and in their mediation of cytotoxic reactions (Richter et al, 1990). It was also shown that the null cells (or the B cells), precultured for 3 days, did not show any functional properties characteristic of B cells (or null cells) (Richter et al, 1990); B cells synthesized and secreted immunoglobulins even if the null cells were added to the cultures as late as day 6 of the 7-day culture (Richter etal.,\ 990).…”