INADEQUATE ANTI-POLYSACCHARIDE ANTIBODY-RESPONSES IN THE CHICKEN

Chickens are notorious for the fact that they carry bacteria such as S almonellae and Campylobacter, which can cause zoonoses by contaminatio n of the end product, without hampering growth and development of the chicken itself. This carrier status can only been explained by the ina bility of the chickens immune system to eliminate the pathogen, this i n turn being due to insufficient humoral responses towards the polysac charides of the bacterial capsule. In a previous study, we demonstrate d that in chickens a model thymus-independent type 2 (TI-2) polysaccha ride antigen, trinitrophenylated Ficoll (TNP-Ficoll), hardly evokes a humoral immune response. Furthermore this TI-2 antigen was shown to ex hibit a very specific initial localization pattern after intravenous i njection, i.e, in the periellipsoidal lymphocyte sheaths (PELS) and th e surrounding ring of macrophages. The functional equivalent of these macrophages in mammals, the marginal zone macrophages, were shown to s uppress the humoral responses against TI-2 antigens. Therefore we inve stigated whether other standard TI-2 antigen models also induce low an tibody responses, whether this low response is dose-dependent, and whe ther macrophages are responsible for this low response. It was found t hat other TI-2 antigens, such as hydroxyethyl starch and detoxified li popolysaccharides, also induced very low IgM and IgG responses, indica ting a general phenomenon that could not be overcome by using a higher dose of antigen. In addition, selective depletion of splenic macropha ges with liposomes containing dichloromethylene diphosphonate prior to immunization increased the specific humoral response to TD and TI-1 a ntigens, but failed to do so for TI-2 antigen. This result indicates t hat the low humoral responses are not (only) due to a macrophage suppr essive activity but also to other yet unknown mechanisms, for example the lack of responsive B cells in the splenic PELS.