Susceptibility to infection with Mycobacterium avium is paradoxically correlated with increased synthesis of specific anti-bacterial antibodies

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Abstract
A comparison was made between the levels of splenic and Intestinal (Peyer's patches and thin Intestinal epithelium) Igproduction of C57BL/6 germ free and conventional C57BL/6, BALB/c, DBA/2 and C3H/He mice and the susceptibility to Mycobacterium avium Infection, evaluated by the number of bacterial colony-forming units (CFU) found in the liver and in the spleen of the animals. Mice received an i.p. Injection of either 5 × 106, 107 or 108 bacteria, or were given the larger inoculum intragastrically. Alternatively, mice were treated with an i.p. injection of M. avium bacterial sonicates. A marked increase of splenic IgA production, quantitatively associated with the size of the inoculum and thus with the degree of infection, was observed in susceptible compared to relatively resistant mice. This increase was observed at an earlier time following infection with the larger rather than with the smaller inocula. Consistent significant increases in splenic production of IgG Isotypes were only observed In the susceptible mice after infection with the intermediate and larger inocula whereas a comparative increase of IgM was only clearly observed after infection with the larger inoculum. Intestinal Ig production remained unchanged, however, in both susceptible and relatively resistant mice after I.p. Infection. Also, all mice were resistant toM. avium infection by the intragastric route and with this site of entry splenic and intestinal Ig production remained unchanged. Susceptibility to M. avium infection was also quantitatively associated with increased levels of circulating specific anti-bacterial antibodies. That higher specific antibody responses observed in susceptible mice were not due to the increase of available antigenic material is shown by the fact that higher specific Ig production was also observed In the susceptible strains after injection of M. avium sonicates. Moreover, higher antibody response seems to be associated with susceptibility because the I.p. administration of serum containing specific Ig to resistant C3H/ He strains increased the number of splenic bacterial CFU recovered at day 15 following l.p. infection with 108M. avium by a factor of almost ten.

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