Adverse effects of antibiotics on the development of gut-associated lymphoid tissues and the serum immunoglobulins in chickens.

: Study was done of the distribution and relative densities of immunoglobulin (Ig)M-, IgG-, and IgA-producing cells in the gut-associated lymphoid tissues and the spleen (SP) of control and antibiotic-treated chickens between 3 and 28 days of age. Specific Ig in the serum also were quantitated simultaneously. Antibiotic treatment included preincubation dipping of fertile eggs in gentamicin solution (500 mg/L), injection of chicks with gentamicin (0.2 mg/chick, subcutaneously), and inclusion of chlortetracycline in the diet (200 mg/kg). At 3 days, the gut-associated lymphoid tissues of control chicks carried few Ig-positive cells, except the bursa of Fabricius in which all 3 classes of Ig-bearing cells were present in relatively large numbers. The SP had few,but equal, numbers of IgM- and IgA-positive cells at this age. As control birds grew older, IgM-positive cells dominated in the SP, followed by the IgA cells. Cell populations fluctuated in the bursa of Fabricius of chicks until 21 days of age when IgM and IgA cells stabilized at a higher density than the IgG-positive cells. The cecal tonsils had no Ig-positive cells at 3 days, mostly IgM cells by 7 days, but equal numbers of the 3 types of cells by 28 days. The large intestines had few IgM-positive cells at 3 days and no IgG cells at 3 or 7 days. The numbers of IgM and IgA cells were approximately equal in the large intestine of the chicks from 7 days until 28 days. Maternally acquired IgG predominated in sera of chicks until 14 days of age, followed by the IgM. At 28 days, 'there was more IgM in the serum than IgG. Serum IgA was not detectable until 14 days of age, and its concentration remained at a lower level than IgM or IgG values. Antibiotic-treated chickens generally carried lower densities of Ig cells than did the respective controls. However, statistically significant (P < 0.05) differences were apparent only with respect to Ig cell populations in the cecal tonsils and the large intestines. The treated chickens also had significantly lower serum IgM concentrations at 28 days of age.