Characterisation of a resource population of pigs screened for resistance to salmonellosis.

The degree of resistance to Salmonella choleraesuis infection in a reference family purposely bred to map resistance genes was assessed. Aspects of the innate and specific immune system were studied to find a parameter that might predict the resistance of pigs to salmonellosis. The family was bred from commercial full-sister pairs of F1-gilts and four boars. One boar (G398) was identified as breeding susceptible offspring, and one boar (G402) as breeding resistant offspring on the basis of pyrexial responses and numbers of Salmonella in liver and spleen post mortem. The other two boars were classified as 'possible resistant' (Y2008) and 'unknown' (Y6101) respectively. Functional differences in immune cells (neutrophils and lymphocytes) between the offspring of G398 and G402 were detected. The most resistant piglets had a higher number of circulating neutrophils and better polymorphonuclear neutrophils (PMNs) function, but a lower mitogenic response of lymphocytes both pre- and post-infection and a lower antibody response. Between the offspring groups of Y2008 and Y6101 no differences were found in the number of viable Salmonella in liver and spleen at post mortem or in immune cell function, however, the survival rate of these offspring groups was clearly different. Twenty three percent of the Y2008-offspring and 33% of the Y6101-offspring reached the predetermined humane clinical endpoint before the end of the experiment. Our findings suggest a role for several inherited immunological traits, including PMN function and lecithin-induced mitogenic proliferation, which appear to influence resistance to salmonellosis.

The B cell compartment of two chicken lines divergently selected for antibody production: differences in structure and function.

In the present study differences in the B cell compartment of two chicken lines selected for either high (H) or low (L) antibody response to sheep red blood cells (SRBC) are investigated. In non-immunized chicks, flow cytometry revealed generally more circulating Ig+ leukocytes in the H line, while in the L line slightly more CD4+ and in week 5, more CD8+ cells were found. In the L line spleen more CD8+ were found and in the H line spleen more CD4+ cells. In week 6, half of the chicks were immunized. Both lines were similarly affected by immunization. Immunization reduced the percentages of the circulating T cell subpopulations, while Ig+ cells were enhanced, compared with non-immunized chicks. Histological determinations with specific mAbs on spleens of young, non-immunized chicks, showed large dense T cell areas in the L line, while in the H line more and larger germinal centres were found. In the H line, also, more B cells were found in the peri-ellipsoid lymphoid sheaths (PELS). No line differences in mononuclear phagocytes were found other than associated with line differences in numbers of PELS and germinal centres. After immunization with TNP-BSA, both higher numbers of TNP-specific antibody producing cells and higher levels of circulating antibody were found in the H line. Moreover, more TNP-specific plasma cells were found in non TNP-immunized H line chicks, than in the L line chicks. The H line had also higher ELISA-titers to KLH 5 days after immunization with KLH. Therefore it was concluded that selection for antibody response has affected the B cell compartment. The H line has relatively more B cells and the splenic structure of the H line differs from the L line, in the H line probably resulting in a more optimal organization for antibody response to T cell dependent antigens.

Differences in distribution of lymphocyte antigens in chicken lines divergently selected for antibody responses to sheep red blood cells.

The proportion of cells showing differentiation antigens specific for T cells, B cells and leukocytes was studied at various ages in peripheral blood, and at 14 weeks of age in the bursa of Fabricius, spleen and thymus of two lines of chicken that had been selected over 13 generations for either high (H) or low (L) antibody responses to sheep red blood cells (SRBC), and also in a randombred control (C) line. Flow cytometry showed no consistently significant differences between the three lines in numbers of circulating lymphocytes and other leukocytes after hatching. However, higher percentages of CD4+ cells and B cells were present in the spleen and thymus from the H line compared with the L line. However, the L line was characterized by a higher proportion of splenic CD8+ cells and spleen cells expressing gamma-delta T-cell receptors. Immunization with sheep red blood cells had no effect on the distribution of CD4+ or CD8+ cells in the various tissues at 2 and 7 days after immunization. These results suggest that previously reported differences in in vivo immune responses between these chicken lines may be related to the differences in resident T-lymphocyte subpopulations in the lymphoid tissues. The involvement of T-cell subsets and non-antigen-specific mechanisms in divergent selection on humoral immune responses in chickens is discussed.

Phagocytic activity of two lines of chickens divergently selected for antibody production.

Differences in phagocytic capacity of two chicken lines selected for high (H) or low (L) antibody response against sheep red blood cells (SRBC) were studied in 8 month old cocks of the seventh selection generation. The H line cocks had significantly higher agglutinin titers after immunization with SRBC than the L line. The total clearance capacity of the phagocytes, measured by the clearance of carbon particles from the blood, did not differ between the lines. The L line cocks had more circulating granulocytes. However, the granulocytes of the H line phagocytized more yeast cells than those of the L line. Neither in immunized nor in non-immunized cocks, were line differences found in the intracellular destruction of antigen by phagocytes, estimated as the superoxide production during phagocytosis and the plasma levels of lysozyme activity and acid phosphatase, before and after immunization. It was concluded that the line difference in antibody response was not due to measurable differences in phagocytic activity.

In vitro T cell activity in two chicken lines divergently selected for antibody response to sheep erythrocytes.

Four experiments were conducted to determine possible differences in the in vitro concanavalin A (ConA) response between two lines selected either for high (H) or low (L) antibody response 5 d after intramuscular immunization with SRBC. In all four experiments, the cell proliferation after stimulation with ConA was higher, although not always significantly so, in the L line than in the H line, independently of dose of Con A and source of lymphocytes. It can be concluded that selection for anti-SRBC antibody response affected the cellular response in chickens. Previously reported results, in other chicken lines selected for humoral response to SRBC after intravenous immunization with SRBC, showed an opposite line difference in mitogen response. These opposite results point to the fact that comparable selection protocols for immunological variables do not necessarily have a comparable influence on the diverse components of the immune response.

Effects of route of immunization, adjuvant and unrelated antigens on the humoral immune response in lines of chickens selected for antibody production against sheep erythrocytes.

Effects of intramuscular (i.m.), intravenous (i.v.) and intraperitoneal (i.p.) primary immunization with the T-dependent antigen, sheep red blood cells (SRBC), was studied in two chicken lines selected for either high (H) or low (L) antibody response after i.m. immunization with SRBC. The primary route of immunization affected the line differences in the primary response and in the secondary response after i.m. reimmunization. Intravenous immunization with the T-dependent antigen bovine serum albumin (BSA) showed line differences similar to those found after i.m. or i.v. immunization with SRBC. Immunization with both the partially T-independent antigens Brucella abortus (BA) or Salmonella H-antigen (SHA) revealed no line effect. Immunization with SRBC in incomplete Freund's adjuvant (IFA) did not change the difference between lines, whereas immunization with complete Freund's adjuvant (CFA) diminished the difference between lines. It is postulated that differences in antibody production between the selected lines might be attributed to differences in T-cell activity.

Effect of different doses of sheep erythrocytes on the humoral immune response of chicken lines selected for high or low antibody production.

A study was conducted to determine the influence caused by the dose of sheep red blood cells (SRBC) on the humoral response of chicken lines selected for high (H) or low (L) antibody production to SRBC. The chicks were of the 5th selection generation. Both sexes were used. The primary doses of SRBC used were: 5 x 10(-4), 5 x 10(-3), 5 x 10(-2), 25 x 10(-2), and 5 x 10(-1) mL packed cells, suspended with phosphate-buffered saline (PBS) to 1 mL, and injected intramuscularly (im). All chicks were reimmunized im with 5 x 10(-1) mL packed cells in 1 mL of PBS. Throughout the experiment, H line chicks had higher titers than L line chicks. The level of primary total and 2-mercaptoethanol (2ME)-resistant titers followed the dose level. However, in total titers, the interactions between line and dose were seen at days 3 and 5 postimmunization. This was caused by a deviation in the ranking of the doses in the L line. Moreover, the kinetics of the primary response differed between the lines. Generally, in H line the peak number for the titers was reached earlier in the response period. The optimum response in terms of the total number of titers in the secondary response generally was inverse to the primary dose level. However, from Day 7 of the secondary response onward, the dose effects were influenced by line. For Line L, no effects for dose on the responding antibody level was seen. The 2ME-resistant titers followed the dose level in the secondary response.(ABSTRACT TRUNCATED AT 250 WORDS)

Interference with the humoral immune response in diverse genetic lines of chickens. II. The effect of colloidal carbon.

Two experiments were conducted to study the difference in humoral immune responses between lines of chickens selected for high (H) or low (L) antibody production to sheep red blood cells (SRBC). Prior to i.v. immunization with SRBC or Brucella abortus (BA), chicks of both lines were injected with either 2, 3 or 4 ml carbon suspension (59 mg carbon/ml) per kg body weight; controls were not injected. In both the H and L line, a higher dose of carbon showed a more progressive depression of the total antibody titer to SRBC during the initial stage of the primary response. The 2ME-resistant antibody titers to SRBC showed the same tendency during the latter phase of the primary response. However, chicks treated with 3 ml carbon had lower 2ME-resistant antibody titers than any other group. Following i.m. reimmunization with SRBC, the previous treatment with carbon doses enhanced total antibody titers throughout the secondary response, when compared to the controls. The 3 ml carbon-treated chicks had the highest total anti-SRBC titers in the secondary response. The secondary 2ME-resistant anti-SRBC titers were not affected by the carbon doses. Carbon treatment did not affect the antibody titers to BA. No differences between the H and L line were found in the effects of carbon on the humoral immune responses to SRBC or BA.

Interference with the humoral immune response in diverse genetic lines of chickens. I. The effect of carrageenan.

Two experiments were conducted in which the effect of carrageenan (CGN) on humoral immune response of chicks selected on either high (H) or low (L) antibody production to sheep red blood cells (SRBC) was determined. H and L line chicks were injected i.p. with different doses of CGN prior to immunization with SRBC or Brucella abortus (BA). Four weeks later chicks were reimmunized with the same antigens. In general, control H and L chicks had significantly higher total anti-SRBC titers than CGN-treated chicks in primary response. Also, total anti-BA titers were significantly higher in control chicks than CGN-treated chicks on days 3 and 5 following primary immunization and on days 0 and 7 of the secondary response. Overall, the 2-mercaptoethanol (2ME)-resistant anti-SRBC titers did not differ significantly among the CGN-treated groups. However, control chicks tended to have higher anti-BA 2ME-resistant titers from day 14 p.i. of primary response on. Regardless of antigen or CGN treatment, the H line chicks had significantly higher titers than L line chicks. However, the CGN treatments did not affect the antibody response to BA nor to SRBC differently between L and H line chicks. It would appear that since CGN is cytotoxic for macrophages, selection for antibody production did not result in different abilities of the macrophages of these chicken lines to respond to an antigenic challenge.