POLYCLONAL B-CELL ACTIVATOR WITH ESTEROLYTIC ACTIVITY AND POLYCLONAL GAMMOPATHY INDUCED BY ALLOGENEIC CELLS IN RABBITS

Abstract

A factor associated with .alpha.-macroglobulin (.alpha.M) which behaves in an Ig-turnover assay as any T-independent antigen or polyclonal B-cell activator (PBA) can be induced in vivo by inoculating rabbits with allogeneic lymph node cells (Al-LNC) or with sheep red blood cells (SRBC). Before inoculation and 3 days after inoculation, the PBA activity was not detected in the serum. PBA appeared and reached a maximum on day 4, decreased gradually after 1 wk and became undetectable to 6-7 wk. The PBA titer for rabbits inoculated with Al-LNC with 100-1000 times higher than for rabbits inoculated with SRBC. The PBA activity was associated entirely with the .alpha.M fraction. The .alpha.M separated from normal rabbit serum had no PBA activity but when normal .alpha.M was complexed with trypsin, a high PBA titer was obtained. Trypsin had PBA, proteolytic and esterolytic activity but when it was bound to .alpha.M, it lost its proteolytic activity and maintained its esterolytic and PBA activity. The PBA activity of the normal .alpha.M-trypsin complex and of the .alpha.M from Al-LNC injected rabbits were inhibited by serine protease inhibitors of low MW, such as aprotinin and phenylmethylsulfonyl fluoride, but not by an inhibitor of high MW such as soybean trypsin inhibitor. The inhibition of PBA activity correlated with the loss of esterolytic activity. For the rabbits inoculated with Al-LNC, the IgG concentration increased in the serum to a 4-fold maximum at 3-5 wk. Evidently the PBA induced in vivo by allogeneic stimulation is an .alpha.M-serine protease complex which appears in the serum; this is followed by a transitory polyclonal gammopathy.