Humoral responses in rabbits immunized with two fractions of Haemonchus contortus: the antigen specificity of such antibodies.

Humoral responses were examined in rabbits immunized with either 28-40 kDa (Fraction 1) or a 19-24 kDa (Fraction 2) antigenic fraction from soluble antigens (Sol L3 Ag) from infective larvae (L3) of Haemonchus contortus. These fractions were eluted from electrophoretically separated Sol L3 Ag. Immunoblots revealed antibodies to Fraction 1 (fr. 1) or Fraction 2 (fr. 2) polypeptides as well as to several other molecular weight polypeptides of the Sol L3 Ag. The latter antibodies were shown by absorption studies not to be Sol L3 Ag cross-reactive anti-bacterial rabbit antibodies. When Sol L3 Ag was affinity-purified using monoclonal antibody to phosphorylcholine (PC) and the resulting fractions were further analysed by immunoblotting using rabbit anti fr. 1 or anti fr. 2 antiserum, the PC antigen was found to be shared between fr. 1 and other polypeptides of Sol L3 Ag. Using the rabbit antibody fractions eluted from nitrocellulose membranes containing fr. 1 or 2 polypeptides, it was found that these fractions contained antibody that bound mainly to fr. 1 and only to fr. 2 polypeptides of Sol L3 Ag. It is concluded that, from the present immune rabbit sera, antibodies specific for either fr. 1 or fr. 2 may be isolated and then used to purify small amounts of the corresponding antigens.