Nathaniel F. Pierce

Bacterial Characteristics and Follicle Surface Structure: Their Roles in Peyer’s Patch Uptake and Transport of Vibrio cholerae

Structural and functional specializations in the intestinal mucosal barrier over Peyer’s patches facilitate contact with and uptake of adherent luminal particles and soluble molecules. These specializations include local reduction in mucus-secreting goblet cells, interruption of the muscularis mucosae by lymphoid follicles(which may alter mucosal motility), and the presence of M cells. M cells are epithelial cells with irregular, widely spaced microvilli, reduced or absent lysosomes, an active transcellular transport system, and a pliable basolateral surface usually invaginated by lymphoid cells. At their luminal surfaces M cells form coated and uncoated vesicles, which are transported to intercellular spaces in the follicle epithelium where initial contact of intestinal antigen and lymphoid cells occurs. The mucus blanket which lies across the microvilli of enterocytes (intestinal absorptive cells) is broken over M cells, allowing microorganisms and particles to approach M cell luminal membranes. Studies with labeled lectins have demonstrated a thin but detectable glycocalyx coat on M cell membranes. Sugars detected by these lectins include beta-D-galactose (Ricinus communis agglutinin), sialic acid and N-acetyl-D-glucosamine (wheat germ agglutinin), but not alpha-D-mannose or alpha-D-glucose (Con A binds only sparsely). Cationized ferritin distributes evenly on M cell luminal membranes indicating that anionic sites are present.

ORAL IMMUNIZATION AGAINST EXPERIMENTAL CHOLERA: THE ROLE OF ANTIGEN FORM AND ANTIGEN COMBINATIONS IN EVOKING PROTECTION*

Two lines of evidence strongly suggest that immunization for cholera should be given orally, aiming to evoke a protective sIgA response in the small intestine. First, the infection is superficial. Ingested Vibrio cholerae adhere to the small bowel mucosa, multiply, and release a protein enterotoxin that acts directly on mucosal cells to cause fluid secretion. Secretory antibody [mostly sIgA] is the only immunologic effector known to act at the mucosal surface or within the gut lumen, where these events can be interrupted. Second, an enteric mucosal sIgA response is probably best stimulated by locally applied antigen. Immature B-cells precommitted to synthesis of IgA are especially numerous in gut-associated lymphoreticular tissue and are efficiently exposed to luminal antigens by a specialized mucosal antigen sampling mechanism? By contrast, parenteral immunization is usually inefficient at evoking mucosal sIgA responses, and may actually suppress them? Some progress toward a practical oral cholera vaccine has been made using live avirulent mutants of V. cholerae or nonliving antigens, but a product combining safety, efficiency, and efficacy has not been achieved. Among the antigens produced by V. cholerae, cholera toxin (CT), or its derivatives, have been most extensively studied as immunizing materials. Cholera toxin is a potent mucosal immunogen; small amounts applied to intestinal mucosa cause vigorous local sIgA-antitoxin responses and protect experimental animals against oral

Oral Immunization for Cholera: Mucosal Antitoxic Immunity is Important and can Probably be Safely Achieved

There is now much evidence to support the notions that secretory IgA antibody is the first line of immunologic defense of the intestinal mucosa and that a mucosal IgA response is best stimulated by antigens applied to the mucosal surface. On this basis, it has been argued that immunization against cholera, a superficial mucosal infection, should be given orally with the aim of evoking a protective mucosal IgA response (1). Some progress in this direction has been made using either live avirulent mutants of V. cholerae or nonliving antigens derived from this organism (2,3).

The role of antigen form and the induction of an intestinal immune response to cholera toxin/toxoid in rats.

Recent efforts to immunize against cholera have focused upon the protective role of antitoxin. We have studied the intestinal immune response to cholera toxin and toxoid in rats with two aims; first, to describe basic features of the secretory immune system of the gut using cholera toxin and toxoid as antigenic probes, and second, to provide an experimental basis for further efforts to induce antitoxic immunity in man.