Research note: effects of age and immunization interval on the anamnestic response to T-cell-dependent and T-cell-independent antigens in chickens.

Measurement of a humoral anamnestic response is a common procedure used to evaluate immunological competence. The purposes of the present study were to determine the optimum time period between primary and secondary immunizations needed to obtain the maximum antibody titer and to determine whether this interval differs with the age of the chicken or with the type of inducing antigen. The anamnestic responses of birds of two ages to a T-cell-dependent antigen (SRBC) and to a T-cell-independent antigen (Brucella abortus, BA) were evaluated. Birds of 4 wk or 6 mo of age were injected i.v. with either BA or SRBC, and a secondary injection was given 2, 4, 6, or 8 wk later. Agglutination titers for total and mercaptoethanol (ME)-resistant antibodies were determined from serum samples collected at 3, 6, and 9 days postsecondary immunization. Generally, titers were highest at 6 days postsecondary immunization. For both antigens, the chick total antibody levels at Day 6 postsecondary immunization were higher at 4-, 6-, and 8-wk immunization intervals than at 2-wk intervals; adult titers were independent of immunization interval. There was an interaction between age of birds and type of antigen.