T lymphocyte reactivity to glutamic acid-alanine-tyrosine in vitro does not reflect antibody response in vivo

Host inflammatory response governs fitness in an avian ectoparasite, the northern fowl mite (Ornithonyssus sylviarum)

Vertebrate immune responses to ectoparasites influence pathogen transmission and host fitness costs. Few studies have characterized natural immune responses to ectoparasites and resultant fitness effects on the ectoparasite. These are critical gaps in understanding vertebrate-ectoparasite interaction, disease ecology and host-parasite co-adaptation. This study focused on an ectoparasite of birds--the northern fowl mite (NFM) (Ornithonyssus sylviarum). Based on prior evidence that chickens develop resistance to NFM, these experiments tested two hypotheses: (i) skin inflammation blocks mite access to blood,impairing development, reproduction and survival; and (ii) host immunogenetic variation influences the inflammatory response and subsequent effects on the ectoparasite. On infested hosts, histology of skin inflammation revealed increased epidermal cell number and size, immigration of leukocytes and deposition of serous exudates on the skin surface. Survival of adult mites and their offspring decreased as the area of skin inflammation increased during an infestation. Inflammation increased the distance to blood vessels beyond the length of mite mouthparts (100-160 lm) and prevented protonymphs and adults from reaching a blood source. Consequently, protonymphs could not complete development, evidenced by a significant inverse relationship between inflammation and protonymph feeding success, as well as an increasing protonymph/adult ratio. Adult females were unable to feed and reproduce, indicated by an inverse relationship between inflammation and egg production, and decreasing female/juvenile ratio. These combined impacts of host inflammation reversed NFM population growth. Intensity of inflammation was influenced by the genotype of the major histocompatibility complex(MHC), supporting previous research that linked these immunological loci with NFM resistance. Overall, these data provide a model for a mechanism of avian resistance to an ectoparasitic arthropod and the fitness costs to the parasite of that host defense.

Effect of genetic selection and MHC haplotypes on lymphocyte proliferation and interleukin-2 like activity in chicken lines selected for high and low antibody production against sheep red blood cells

Chickens from third generation matings of lines of chickens selected for high (HA) and low (LA) antibody production to sheep red blood cells (SRBC) and typed for MHC genotypes B13/13, B13/21, and B21/21 were used in this study. Chickens from both lines carried all the three genotypes B13/13, B13/21, and B21/21. To study T- and B-lymphocytes mitogenic activity, 12-week-old female chickens were injected intravenously with 0.2 ml of 9% SRBC and spleens were collected at 0, 6 h, and 6 day post-antigen injection (pAg). Isolated lymphocytes were incubated with either Concanavalin-A (Con-A) for T-cell activity, or Pokeweed mitogen (PWM) for B-cell activity and thymidine 3H uptakes were measured. To study the Interleukin-2 (IL-2)-like activity in the same lines and genotypes, splenic lymphocytes from 12-week-old chickens were passed through nylon wool columns to enrich the T-cell population. After a 24 h incubation with Con-A, the conditioned media (CM) were collected. The CM were tested for IL-2 like activity by determining whether they altered the proliferation of Con-A stimulated T cells. This proliferation effect was then compared to that of a reference conditioned media (RCM) prepared from K-strain birds and that were used as the standard for the assay. There was no significant difference (p > 0.05) in IL-2 like activity between HA and LA lines, however, the LA was significantly higher than HA (p < 0.05) in T- and B-cell mitogenic activity. The genotype B13/13 had significantly higher (p < 0.05) IL-2 like activity than the B21/21. The genotype B13/13 was also significantly higher (p < 0.05) in T- and B-cell mitogenic activity than the B21/21. At 0 h, pAg T- and B-mitogenic activity was significantly higher (p < 0.05) than 6 h. In summary, our results indicate that although the birds were selected for high antibody production to SRBC, their lymphocyte mitogenic activity was lower than those selected for low antibody production. Hence, humoral and cell-mediated immune responses appear to be under different genetic controls, and that selection for greater humoral response may be at the expense of cellular responses. Our results also suggest differences in IL-2 like activity production between chickens carrying different MHC B-haplotypes, and that genetic control of such activity is possibly linked to the MHC genes.

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.

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.