Stimulation of active K+ transport by anti-L antibodies in trypsin- treated low potassium sheep erythrocytes

Dear Sir: In this letter we attempt to resolve a discrepancy on the effect of trypsin on the sensitivity of low potassium (LK) sheep red blood cells to the anti-L antibody. We had reported the failure of trypsinization to abolish completely sensitivity to the antibody (I). More recently Lauf et al. published in this journal the observation that trypsin could indeed eliminate all sensitivity (10). We show here that red cells of LK sheep homozygous at the locus controlling the LK phenotype respond to trypsinization differently from the way cells from heterozygotes respond. In red cells of the LK phenotype of sheep and goats, the rate of active Na/ K transport is much lower than in red cells of high potassium (HK) animals (7, 11). LK red cells have a membrane-associated blood group antigen, L, which may be responsible for the low rate of transport; alloimmune anti-L serum raised in H K sheep stimulates active Na /K transport several-fold in LK red cells of sheep and goats (5, 6, 9). Lauf et al. (8) showed that, in LK sheep red cells pretreated with trypsin, the N a / K pumps were no longer stimulated by anti-L serum (trypsin had no other effect on cation transport), suggesting selective destruction of the L antigen by trypsin. Anti-L serum also inhibits passive K transport in LK red cells (2, 5). Thus, there are two kinds of specificities in anti-L serum, one called anti-Lp which stimulates the pump, and another, anti-Lt, which inhibits passive transport (1). At the same time two antigen types on the cells can be distinguished; Lp, which is modified by trypsin, and Lt, to which anti-Lt binds, causing inhibition of passive K transport. The Lt antigen is unaffected by trypsin since anti-L serum inhibits passive K transport in trypsin-treated LK sheep cells fully as well as in untreated cells (1, 10). It was suggested previously that treatment of LK sheep cells with trypsin did not completely abolish stimulation of the pump by anti-L serum (1). This observation was tentatively explained in terms of an action of anti-Lt on both pump and passive transport, and was consistent with the failure of extensive absorption of anti-L serum with LK goat cells to remove all stimulatory activity to the pumps of LK sheep cells (1, 7) (LK goat cells should remove anti-Lp much more effectively than anti-Ll). Lauf et al. (10) reexamined the effect of trypsin on the response of LK sheep cells to anti-L, and reported complete abolition of stimulation of the pump in