Sites of synthesis and localization of IgE in rats infested with Nippostrongylus brasiliensis

Abstract

The tissue and cellular localization of IgE has been studied in normal rats and rats infested with the enteric parasite, Nippostrongylus brasiliensis. The results of the study do not support the suggestion that IgE is a secretory immunoglobulin with a physiology analogous to that of IgA. The lamina propria of the small intestine and the colonic and pulmonary mucosal surfaces contain numerous anti-IgE-binding cells, but these have been shown to be mast cells and not plasma cells. The major sites of IgE synthesis were the regional lymph nodes of the small intestine and the lungs, which contained large numbers of IgE-secreting plasma cells. Smaller numbers of IgE-secreting plasma cells were also found in peripheral lymph nodes, some of which were distant from tissues known to have direct contact with either larvae or adult worms. Peyer's patches, the intrapulmonary lymphoid tissue and the spleen contained few, if any, IgE-secreting plasma cells. The significance of the IgE which was readily demonstrated in germinal centres of Peyer's patches and several lymph nodes is not known. In contrast to infested animals, the lymphoid organs of normal rats rarely contained any IgE-containing cells. Thoracic duct lymph from infested animals contained only few IgE-containing large lymphocytes, similar in number to cells containing IgM or IgG but only 1/50 as many as those containing IgA. An unexpected observation was that mast cells in mucosal organs appear to contain intracellular IgE, differing in this respect from connective tissue mast cells. Mast cells lying between epithelial cells, the 'globule leucocytes', also appear to contain intracellular IgE and it is suggested that such cells may be responsible for the presence of IgE in exocrine secretions. This study highlights the need for careful identification of cells appearing to contain IgE and suggests reasons for the widely differing reports of the numbers of IgE-secreting plasma cells in human intestinal biopsies.