Abstract
Immunocytes play a central role in specific and non-specific defence mechanism in chickens. In this study, techniques were established for the in vitro investigation of the phagocytic and bactericidal activities and the release of respiratory burst (RB) metabolites of macrophages and the antigenic responses of chicken splenocytes. The immuno-modulating potential of 1) a filtrate of Salmonella infected RPMI-1640 (SRPMI-1640), 2) supernatants from elicited macrophage cultures (NMΦ) and 3) supernatants from Salmonella infected macrophage cultures (SMΦ) was evaluated. Chicken peritoneal exudate cells (PEC) were elicited by the injection of irritants such as saline, thioglycolate broth and Sephadex G-50. Sephadex G-50 was found to induce the maximum number of PEC. A single dose of Sephadex G-50 recruited 28.1±11.9 X 106 PEC per bird, whilst a double dose recruited 85.5±27 X 106 cells. These PEC contained on an average 50% macrophages irrespective of the chemical nature of the irritant used. The proportion of these macrophages could be enriched to greater than 80% by exploiting their adherent property. The multinucleated giant cell (MGC) formation and fibroblast contamination were common sequelae of extended culture of Sephadex recruited peritoneal exudate macrophage (PEM). Phagocytosis of sheep red blood cells (SRBC) as well as Salmonella gallin-arum was depended on the degree of opsonisation and the time of exposure of the phagocytic particles but was unaffected by the length of time for which the macrohages have been cultured and the nature of particles being phagocytosed. S. gallinarum was phagocytosed by PEMΦ as efficiently as SRBC. There was more killing of phagocytosed opsonised Salmonella than phagocytosed un-opsonised Salmonella. PEMΦ released a detectable amount of hydrogen peroxide and were highly responsive to PMA and 4-O-M-PMA. Moreover, RB activity was influenced by culture age, cell concentration and incubation time of the assay. The splenocytes from NDV vaccinated chickens of the B 21 haplotype showed strong antigen specific proliferation when incubated in vitro with 4-16 μg/ml of NDV antigen. They also produced NDV specific antibodies after 14 days in culture. The proliferation could be effectively measured either by the [3H]-thymidine uptake or by the MTT assay. Anti-NDV antibodies produced by such splenocyte cultures were detected using an ELISA designed to give high level of sensitivity. The SRPMI-1640, NMΦ or SMΦ did not effect the adherence or the phagocytic activity of PEMΦ. However, SMΦ induced a slight reduction in the percentage of PEMΦ phagocytosing non-opsonised SRBC. All these media induced macrophages to release hydrogen peroxide at levels similar to those to PMA. By contrast all these media inhibited both the NDV induced proliferation and the anti-NDV antibody production by chicken splenocytes. This inhibition could be due to products from Salmonella or Salmonella induced activation of macrophages. The inhibition observed with NM may be due to in vitro activation of PEMΦ or due to products from the contaminating fibroblasts.