INCOMPLETE DOMINANCE OF THE LOW ANTIBODY-RESPONSE TO CRYPTOSPORIDIUM-PARVUM ANTIGENS IN MICE SELECTED FOR HIGH AND LOW ANTIBODY RESPONSIVENESS

The humoral antibody response to Cryptosporidium was investigated in m ice genetically selected for high (H) and low (L) antibody responsiven ess. Groups of 4-5 mice from two different selections, general primary (GP) and general secondary (GS), were studied. Following immunization with Cryptosporidium parvum antigens, the maximum levels of IgG in th e H-GP ((X) over bar +/- SD = 1.13 +/- 0.35, N = 5) and in the H-GS (0 .42 +/- 0.15, N = 4) lines, and of IgM in the H-GP line (0.86 +/- 0.53 , N = 5) were significantly higher than those in their L counterparts (0.04 +/- 0.02, N = 5; 0.05 +/- 0.02, N = 4 and 0.24 +/- 0.07, N = 5, respectively). These findings were similar to those reported for other immunogens. However, the IgG (0.22 +/- 0.05, N = 4) and the IgM (0.33 +/- 0.08, N = 4) responses to immunization of F-1 (L(GP) x H-GP) hybr ids indicated an incomplete dominance of the low response, in contrast to the incomplete dominance of the high response described for many o ther antigens and representing an important exception. In addition, th e H, L and F-1 mice did not develop detectable infections when inocula ted with live Cryptosporidium oocysts, supporting the view that a redu ced or zero antibody production itself is not enough to permit the est ablishment of Cryptosporidium infection in adult mice.