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

Humoral and cell-mediated immunities and phagocytic ability were examined a t the third and fourth generations of selection in two pairs of chicken lin es (at 10 wk of age) that were divergently selected for levels of high seru m 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 w k of age. At 20 and 23 wk of age, 20 birds from the respective lines were i njected Brucella abortus (BA), and blood samples were collected at 7 and 14 d postprimary immunization (PPI) and postsecondary immunization (PSI). Pha gocytic ability was measured by carbon clearance assay at 25 and 30 wk of a ge. 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 si gnificantly (P < 0.05) higher total antibody titers to BA than their low co unterparts. Similarly, mercaptoethanol-resistant (MER) antibody titers to B A, 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 gener ations, the HIM and HIC lines had significantly (P < 0.01) faster carbon cl earance ability than the LIM and LIG lines. The results suggest that both p airs of selected lines exhibited divergence in immunocompetence, although t hey had been selected for serum Ig isotypes.