Self, non-self and the immune system

This thesis describes three areas of immunological research: - Firstly the development of an immunological technique which allows an improved detection of cells secreting specific antibodies. The results of this study demonstrated that the use of a protocol employing coated capture antibodies and enzyme-labeled antigen in stead of the sandwich-method employing antigen coating and enzymelabeled detector antibodies could considerably improve the detection of cells secreting antibodies of the lgG isotypes. - Secondly an investigation of the immune system of germfree mice, fed an ultrafiltered chemically defined low-molecular diet. Such mice are considered to be completely free of exogenous antigens. Previous studies have shown that such mice have similar numbers of B cells and background lgM secreting cells as conventional mice, but are highly deficient in background lgG and lgA production. The results of our study demonstrated that such mice had a normal repertoire of functional T cells, that could be induced to lymphokine secretion, and that the absence of background immunoglobulin secreting cells of the non-lgM isotypes was not caused by defects in their B or T cells. This data indicates that the immune system has an autonomous activity, which is independent of exogenous antigenic stimulation. - Thirdly a study on the effects of the manipulation of the immune system with antibodies against MHC class II molecules. The results of this study demonstrated that in vivo treatment with antibodies directed against the MHC class II molecules caused a rapid decrease in the number of background immunoglobulin secreting cells and T cells in the spleen. This indicates that the generation of background immunoglobulin secreting cells and the maintenance of the T cell compartment are dependent on cognate interactions within the immune system involving MHC class II. The combined results from these studies indicate that self-recognition is of great importance for the autonomous activity of the immune system. By defining the immune system as a host-defense system, it has been postulated that the cells involved in this system should react to foreign antigens, but ignore self-molecules. Based on the observation of self-recognition within the system we conclude that host-defense is one among the tasks of the immune system, which could be considered as the molecular equivalent of the nervous system.