Immune responses to eimeria: quantification of antibody isotypes to Eimeria tenella in chicken serum and bile by means of the ELISA.

The enzyme-linked immunosorbent assay (ELISA) has been used to study the serum IgM and IgG response and the bile IgA and IgM response of chickens to a primary, secondary and tertiary inoculation of Eimeria tenella. In the serum there was a rapid and transient IgM response to the primary infection; second and third inoculations of oocysts had comparatively little effect on the concentrations of this antibody isotype. This differed from the specific IgG response which was later and of similar magnitude after each inoculum. In the bile, specific IgA reached its highest concentrations 9-10 days after the primary inoculation and then declined rapidly. The second and third inoculations each induced low concentrations of this isotype. The specific biliary IgM response to the primary inoculation was similar in profile to that of the IgA, but IgM was detected only on day 14-15 after the second and not at all after the third inoculation. The findings are discussed and are compared with the results obtained using other host species, principally the rat, and with other gut organisms. The relevance of the antibody response in resistance to eimerian infections is also discussed.