“…Although mixtures of gut microbial species, each successfully cultivated in vitro, have been shown to stimulate the development of IgA plasma cells in gut LP of formerly GF mice to roughly one-half to two-thirds of the levels from that in conventionally reared mice (Moreau et al, 1978), most associations with single gut commensals are far less effective, quantitatively and temporally (Carter and Pollard, 1971;Foo and Lee, 1972;Berg and Savage, 1975;Moreau et al, 1978;Table 18.1). In the last decade, we have appreciated that major elements of the gut flora of mice and of many other animals were obligate anaerobes that have not yet been cultured in vitro (Tannock et al, 1987).…”