Attempts were made to isolate Clostridium difJicile from a total of 431 fecal specimens from 149 young and 213 elderly healthy adults, and 69 elderly adults with cerebrovascular disease but no gastrointestinal disease. C. difJicile was isolated from 49 specimens, and the frequency of isolation was 15.4% in healthy young adults, 7.0% in healthy elderly adults, and 15.9% in elderly adults with cerebrovascular disease. Thirty-four (about 70%) of the 49 C. difJicile strains isolated produced cytotoxin which was neutralized by Clostridium sordellii antitoxin in vitro; in both young and elderly adults approximately 30% of the C. difJicile isolates were nontoxigenic. The mean concentration of C. difJicile in feces was 10 4 • 1/g in young adults and 104.6/g in elderly adults, with a range of 10 2 • 0 to 10 6 • 9/g. Antibody against C. difJicile toxin was found in most of the sera obtained from young adults carrying toxigenic C. difJicile, but not in sera of elderly adults, no matter how abundant was toxigenic C. difJicile in the feces.Toxigenic strains of Clostridium dijfu;ile have been shown to be a major cause of antibiotic-associated pseudomembranous colitis (PMC) of man (1,3,7,8,13). Feces from the vast majority of PMC patients contain a cytopathic toxin which is neutralized by Clostridium sordellii antitoxin, and toxigenic C. difficile in high concentration. Toxigenic strains of this organism have been isolated also at a high rate from feces of healthy neonates and infants (II, 15, 18) but rarely from those of healthy adults (6, 15). Kobayashi et al (14) isolated C. difficile at a high rate from the feces of healthy adults by using a selective medium devised by George et al (5), although there were fewer than 100 of the organisms per gram in most specimens. Recently, Willey and Bartlett (19) also developed a selective medium for the isolation of C. dijfu;ile, but failed to isolate the organism from the feces of healthy adults.Considering that antibiotic-associated PMC or diarrhea occurs more frequently in elderly adults (2, 10), we attempted to determine the frequency of isolation of C. difficile from fecal specimens, the toxigenicity of the isolates, and the presence of antibody against C. dijfu;ile toxin in the sera of young and elderly adults.

The abnormality in myasthenia gravis (MG) is a deficiency of acetylcholine receptors (AChRs) at neuromuscular junctions due to an antibody-mediated autoimmune attack. Although immunosuppressive drugs are usually beneficial in MG, they produce generalized suppression of the immune system. Treatment should specifically inhibit the immune response to AChR. Oral administration of an antigen may induce specific tolerance and has recently been tested for treatment of several cell-mediated experimental and human autoimmune diseases. In this study, we investigated the effects of oral administration of AChR in an experimental rat model of MG (EAMG), which is antibody mediated. Lewis rats were fed various doses of purified or unpurified Torpedo AChR, or a control antigen, ovalbumin (OVA). They were then immunized with AChR or OVA. We measured antibody responses to Torpedo AChR or OVA, autoantibody responses to rat AChR, cellular responses, cellular suppressive effects, and clinical status. Our results showed that AChR feeding prevented clinical signs of EAMG. It initially primed, then inhibited, antibody responses to foreign (Torpedo) AChR and self (rat) AChR, with a delayed onset. Cellular responses to AChR, measured by lymphocyte proliferation and interleukin-2 production, were markedly inhibited. The effects were dose dependent. Unpurified AChR given in comparable amounts was far less effective than pure AChR. OVA feeding had similar, but even more potent effects on humoral and cellular immune responses to OVA, but did not inhibit clinical EAMG or AChR responses. Moderate nonspecific suppression by splenic T cells from orally treated animals was demonstrated in vitro. We conclude that oral therapy is beneficial in EAMG and may prove effective in MG patients. Early priming and delayed inhibition suggest that a molecule with less immunogenic potential than intact AChR might be more effective as a therapeutic agent.

Because of the antibody-mediated pathogenesis of MG, it is of particular interest to understand the effects of oral administration of the autoantigen AChR on the disease process. It is now clear that feeding AChR prior to immunization can prevent clinical manifestation of EAMG. It initially primed, then inhibited, antibody responses to foreign (Torpedo) AChR and self (rat) AChR, with a delayed onset. Cellular responses to AChR, evaluated by lymphocyte proliferation and IL-2 production, were markedly inhibited. The effects were dependent on the dose and purity of the fed antigen. Tolerance to an orally administered unrelated antigen, OVA, was more prompt in development and more profound, illustrating the influence of the nature of the antigen on tolerance. The tolerance induced was antigen specific. Oral administration of AChR after immunization resulted in inhibition of the clinical manifestation of EAMG, concomitant with a paradoxical enhancement of the AChR-antibody responses. Both the clinical benefit and the antibody response appear to be dependent on the feeding protocol. These findings suggest that a molecule with less immunogenic potential than native AChR may be required for safe and effective oral treatment of ongoing disease.