Expression of Fcμ receptors by human T lymphocytes: Effects of enzymes, metabolic inhibitors, and X-irradiation
Immunoglobulin Heavy Chains
The expression of Fcμ receptors by purified human peripheral blood T lymphocytes during culture was studied using a rosette technique with rabbit IgM antibody-coated ox erythrocytes (EOx-IgM). Unbound Fcμ receptors were not detected on freshly isolated purified T cells before or after treatment with 50 U/ml neuraminidase (Vibrio comma). Optimal detection of unbound receptors required culture of viable T cells for 24 hr at 37°C in RPMI-1640 medium with FCS, or in Iscove's medium without FCS. Freshly isolated T cells treated with sodium azide did not express Fcμ receptors, nor did T cells cultured at 4°C. A reduced number of T cells expressed Fcμ receptors after incubation in RPMI-1640 medium without FCS. A direct influence of T cell protein synthesis on Fcμ receptor expression is likely, since T cells cultured with puromycin or cycloheximide or briefly treated with actinomycin D or mitomycin C prior to culture displayed parallel temporal inhibition of EOx-IgM rosette formation and 3H-leucine incorporation. Freshly isolated T cells irradiated with 500 to 5000 R before culture also displayed parallel temporal inhibition of EOx-IgM rosette formation and 3H-leucine incorporation. No impairment of optimal EOx-IgM rosette formation occurred in control T lymphocytes cultured for 24 hr then treated with metabolic inhibitors or x-irradiation before rosetting, which suggests that their effects did not directly influence the receptor-ligand interaction itself. However, treatment of these cultured control T cells with trypsin or IgM but not neuraminidase before rosetting subsequently decreased these cells' EOx-IgM rosette formation. These findings suggest the expression of Fcμ receptors by cultured T cells as detected by EOx-IgM rosette formation is critically dependent on intracellular events, principally protein synthesis, whereas the interaction of receptor and ligand leading to rosette formation is principally dependent on the absence of a competitive ligand, i.e., unbound IgM.