Oral tolerance to ovalbumin in mice: studies of chemically modified and 'biologically filtered' antigen.

Suppression of systemic immunity after the feeding of antigen was investigated in mice by means of serum transfer experiments. Serum collected from mice 1 hr after a single intragastric dose of 25 mg OVA induced suppression of systemic DTH when injected intraperitoneally into recipient mice. This suppression was found to be restricted to the cell-mediated limb of immunity and was antigen-specific. A postulated function of the intestine, conversion of antigen into tolerogenic form by means of intestinal antigen processing, was studied by attempting to mimic intestinal alteration of OVA by chemical modification of the antigen. Parenteral injection of mice with either deaggregated or denatured OVA did not produce the typical pattern of unresponsiveness seen in animals given intestinally processed OVA. Intestinal processing was also shown to be distinct from systemic antigen processing. Mice injected with serum containing systemically 'filtered' OVA did not become tolerant to OVA in the manner of recipients of serum from OVA-fed mice.