Evaluation of the humoral immune response to different antigens in Arkansas Regressor and Progressor chickens

Viewpoint: Measuring the effects of wildlife contraception: the argument for comparing apples with oranges

There are few wildlife populations existing today that can be supported without some form of management. Wildlife fertility control, as one option, has moved from the research stage to actual application with a number of species, including wild horses, urban deer, captive exotic species and even African elephants, but this approach remains controversial in many quarters. Strident debate has arisen over the possible effects of contraception on behaviour, genetics, stress and even management economics, among other parameters. Part of the debate arises from the fact that critics often fail to recognise that some form of alternative management will be applied, and a second problem arises when critics fail to identify and demand the same concern for the consequences of the alternative management approaches. Thus, any rational debate on the merits or possible effects of contraceptive management of wildlife must also recognise all alternative management approaches and apply the same concern and questions to these alternative approaches – including ‘no management’ – as are currently being applied to fertility control. Only then will the stewards of wildlife be in a position to make wise and informed decisions about management options.

Genetic line and major histocompatibility complex effects on primary and secondary antibody responses to T-dependent and T-independent antigens

The effects of MHC and nonMHC (background) genetics on the kinetics of primary and secondary antibody responses to T-cell-dependent (SRBC) and T-cell-independent [Brucella abortus (BA)] antigens were investigated. Eight genetic groups were represented, with four homozygous MHC haplotypes [B1-IrGATlow (IrGAT = immune response to GAT locus); B1-IrGAThigh; B19-Ir-GATlow; B19-IrGAThigh] on two genetic backgrounds, the S1 and G lines. Birds were injected simultaneously with BA and SRBC at 4 and 7 wk of age, and blood samples were taken weekly from 4 to 10 wk of age for measurement of total agglutinating serum antibody levels. A quadratic equation and its first derivative were computed for each bird to approximate individual curve parameters: y max, the maximum titer; t max, the time required to achieve y max; and c coefficient, the rate of decline in the titer. Curve parameters of birds from different lines were analyzed separately by using the General Linear Model procedure. A second analysis that included line effect evaluated the nonMHC gene effects and their interactions with erythrocyte antigen B locus (Ea-B) or IrGAT. In the S1 line, there was an interaction (P < 0.05) between MHC haplotypes and sex for primary response to BA. In contrast, there were no significant main effects nor interactions in the G line background for primary and secondary responses to BA and SRBC. There was an effect (P < 0.05) of line background on y max for primary BA and for secondary SRBC responses. A positive correlation (P < 0.05) was found between the c coefficients of BA and SRBC secondary responses, suggesting that the rate of decline in the secondary response is similar between these T-dependent and T-independent responses. The overall results of this study indicate complex interactions between specific MHC alleles and the nonMHC background of the lines in which they are studied.

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 immunoglobulin M and G levels at 10 wk of age to examine the effect of selection on direct and correlated traits. After three generations of selection, the lines were tested for their ability of antibody production against SRBC, a T cell dependent antigen. At 14 and 17 wk of age, the lines were immunized intravenously with 1 mL of 5% SRBC solution. Blood samples were collected at 7 and 14 d of post primary immunization (PPI) and post secondary immunization (PSI). Selection was effective (P < 0.01) in changing the serum immunoglobulin 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 selection. Selection differentials varied considerably during the selection, but the selection response was almost constant. Realized heritability was relatively 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 significantly (P < 0.01) between the HIM and LIM lines at 7 and 14 d PPI, and 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 PSI. The LIG line had significantly higher total antibody titers to SRBC than 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 immunocompetent cells that modulate the immune response of the selected lines.

Sheep red blood cell and Brucella abortus antibody responses in chickens selected for multitrait immunocompetence

Chickens from replicated lines divergently selected for multitrait immunocompetence were tested for their antibody responses to sheep red blood cells and Brucella abortus antigen. All birds were injected with sheep red blood cells and B. abortus antigens at 4 and 9 wk of age, and blood samples were taken 6, 8, and 10 d postimmunization. Antibody titers were determined by using agglutination assays. For sheep red blood cell responses, the most marked difference was between the high and low lines postsecondary immunization. The high line titer was still rising at 10 d, whereas the low line had reached its peak at 8 d and was decreasing. This may be a result of the selection process in which the high line is selected for a high, persistent response to two T cell-dependent antigens at 3 wk postimmunization. For B. abortus responses, the only differences were between high and low lines postsecondary immunization. The high lines were always higher than the low lines, with differences getting smaller as time postimmunization increased. In summary, selection for multitrait immunocompetence resulted in changes in antibody response to unrelated antigens.