THE V4-34 ENCODED ANTI-I AUTOANTIBODIES RECOGNIZE A LARGE SUBSET OF HUMAN AND MOUSE B-CELLS

Autoantibodies to the i, I and Pr-2 carbohydrate determinants bind red blood cells, preferentially at low temperature in vitro, Using multip arameter flow cytometric analyses, we demonstrate that each of these a utoantibodies also react with human and mouse lymphocytes at physiolog ic temperatures. The anti-Pr-2 autoantibody recognizes a glycoprotein determinant(s) expressed by a subset of both T and B lymphocytes. In c ontrast, the binding of anti-i and anti-I antibodies each is restricte d to B-lymphocytes, The anti-i autoantibody binds to over 50% of all B cells, whereas the anti-I antibody reacts with less than 10% of eithe r tonsillar or blood B cells, Prior studies identified that the B cell isoform of CD45 (B220) has the linear poly-N-acetyllactosamine that f orms the ''i'' determinant, Because anti-B220 antibodies recently have been reported to influence T-dependent B-cell. isotype switching, we tested each antibody for its ability to influence the production of se condary Ig isotypes by murine splenocytes co-cultured with a stimulato r helper T cell clone, We find that addition of anti-i antibody increa ses the proportion of B cells secreting secondary Ig isotypes, In cont rast, the anti-I antibody had no such effect, These findings imply tha t stimulation of B cells through the highly conserved carbohydrate det erminant that forms the ''i'' antigen may be of physiologic importance in T-dependent B-cell differentiation.