The detection of public Ia antigens on the surface of B6-C.H-2bm12 blast cells

The B6-C.H-2bm12 (bm12) strain has previously been described as a spontaneously occurring mutant wherein the parental (C57BL/6 Iab specificities (Ia.3, 8, 9, 15 and 20) are absent or reduced in amount. To further characterize the bm12 mutant the antigenic phenotype of LPS-activated bm12 blast cells was determined with monoclonal and conventional anti-Ia antibodies. By direct testing and absorption the public Ia.8, 9 and 15 specificities were readily detected on both parental C57BL/6 and mutant bm12 blast cells, and the amounts of these antigens on activated bm12 cells were similar to or less than those found on C57BL/6 blast cells. The findings demonstrate that the Ia-I mutation has not resulted in an absolute loss of these specificities, but has altered their expression, or their accessibility to antibody on resting cells. By contrast, the private Ia. 20 specificity and another specificity (designated Iab) could not be detected on bm12 blast cells.