Genetic Analysis of Primary and Secondary Immune Responses in the Chicken

Total agglutinin antibody titers, 2-mercaptoethanol (2-ME) sensitive, and 2-ME resistant antibody titers were determined in 561 White Plymouth Rock chicks. At 38 days of age chicks were intramuscularly injected with .25 ml packed sheep red blood cells (SRBC) and at 66 days of age with .5 ml SRBC. Antibody titers were determined on Days 0, 3, 5, 7, and 10 post-injection. Mean total titer (5.2, log2 value) was highest on Day 7 for the primary response and the secondary response peak titer (7.0) was measured on Day 5. The primary response was characterized by a very low level of 2-ME resistant antibodies. The secondary response consisted of both types of antibody. The heritability estimates indicate that selection for total antibody titer of the primary response can be based on the titer level of Day 5 postinjection (h2s = .39). For the secondary response, Days 3 (h2s = .34) and 5 (h2s = .28) postinjection can be considered. Phenotypic correlations between total antibody titers of first and second injection are not significant on Days 5, 7, and 10 post second injection. The negative relationship between primary and secondary 2-ME sensitive antibody titers in contrast with a positive relationship between primary 2-ME sensitive antibody titers and secondary 2-ME resistant antibody titers explains this result. Additive genetic correlations between total antibody titers of first and second injection tend to be quite negative on Days 5, 7, and 10 post second injection. Selection for an improved prophylactic response, therefore, appears to be not easily achieved either via selection of parameters of the primary immune response or via the secondary response.