Direct and correlated response to divergent selection for serum immunoglobulin M and G levels in chickens

Two pairs of chicken lines were divergently selected for serum immunoglobul in M and G levels at 10 wk of age to examine the effect of selection on dir ect and correlated traits. After three generations of selection, the Lines were tested for their ability of antibody production against SRBC, a T eel dependent antigen. At 14 and 17 wk of age, the lines were immunized intrave nously with 1 mt of 5% SRBC solution. Blood samples were collected at 7 and 14 d of post primary immunization (PPI) and post secondary immunization (P SI). Selection was effective (P < 0.01) in changing the serum immunoglobuli n M levels. The G levels were changed in a downward direction initially in the high line. The differences between the high immunoglobulin M (HIM) and low immunoglobulin M (LIM) Lines as well as high immunoglobulin G (HIG) and low immunoglobulin G (LIG) lines became larger during the course of select ion. Selection differentials varied considerably during the selection, but the selection response was almost constant. Realized heritability was relat ively high, ranging from 0.58 to 0.66 and from 0.40 to 0.60 for the IgM and IgG selected Lines, respectively. Total antibody titers to SRBC differed s ignificantly (P < 0.01) between the HIM and LIM lines at 7 and 14 d PPI, an d 7 d PSI. The HIM line also produced significantly higher mercaptoethanol resistant antibody titers to SRBC than the LIM line at 7 and 14 d PPI and P SI. The LIG line had significantly higher total antibody titers to SRBC tha n the HIG line at both 7 and 14 d of PPI and PSI. From these results, it is suggested that selection of chickens on the basis of serum immunoglobulin isotypes may change antibody producing cells as well as other immunocompete nt cells that modulate the immune response of the selected lines.