Cell-mediated and humoral immunity and phagocytic ability in chicken Lines divergently selected for serum immunoglobulin M and G levels

Humoral and cell-mediated immunities and phagocytic ability were examined at the third and fourth generations of selection in two pairs of chicken lines (at 10 wk of age) that were divergently selected for levels of high serum Ig M (HIM), low serum Ig M (LIM), high serum Ig G (HIG), and low serum Ig G (LIG). Cell-mediated immunity was examined by splenomegaly assay at 12 wk of age. At 20 and 23 wk of age, 20 birds from the respective lines were injected Brucella abortus (BA), and blood samples were collected at 7 and 14 d postprimary immunization (PPI) and postsecondary immunization (PSI). Phagocytic ability was measured by carbon clearance assay at 25 and 30 wk of age. The results showed that the LIG line had higher degree of splenomegaly indices than the HIG line in both generations. The HIM and HIG lines had significantly (P < 0.05) higher total antibody titers to BA than their low counterparts. Similarly, mercaptoethanol-resistant (MER) antibody titers to BA, as measured only in the fourth generation, were significantly (P < 0.05) higher in the HIM and HIG lines than their low counterparts. In both generations, the HIM and HIG lines had significantly (P < 0.01) faster carbon clearance ability than the LIM and LIG lines. The results suggest that both pairs of selected lines exhibited divergence in immunocompetence, although they had been selected for serum Ig isotypes.