Immunity to intestinal parasites: role of mast cells and goblet cells

Nippostrongylus brasiliensis infection of rats and mice is a model for studying immunity at mucosal surfaces. Adult worms are spontaneously expelled from the intestine at the end of the second week of infection. Expulsion from the jejunum requires the presence of immune T lymphocytes and IgG antibodies. Mucosal mast cells (MMCs) are a prominent part of the jejunal inflammatory response. They are derived from a hematopoietic stem cell, possibly the same precursor as basophils. Their differentiation is not absolutely T dependent but their accumulation at the site of infection is. The possible involvement of IgE antibodies and intestinal MMCs through a "leak lesion" is still uncertain. Increased mucus secretion from epithelial goblet cells is also a prominent feature of the inflammatory reaction at the site of infection. Goblet cell numbers increase two to four times at the onset of worm expulsion; this increase is regulated by T lymphocytes and possibly immune serum. The mechanism of mucus secretion in these infections is not clear; it may be a response to mast cell mediators. Together with antiworm antibodies, intestinal mucus may trap worms and prevent them from surviving in the intervillous spaces of the jejunum. Thus, expulsion of this intestinal parasite may occur through a nonspecific process that is induced by specific immune mechanisms.