The effect of protein malnutrition on the IgA immune response in mice.

The influence of protein malnutrition on the IgA immune response was determined in BALB/c mice fed isocaloric diets containing 20% (control), 4%, or 2% protein. We describe here a severely protein-deficient state (6 weeks on a 2% protein diet) and a moderately malnourished state (6-8 weeks on a 4% protein diet). The total IgA concentration in intestinal washes, as determined by radial immunodiffusion, was reduced at 6 and 8 weeks in the 4% diet group and at 6 weeks in the 2% diet group, compared to the controls. Serum IgA levels were significantly elevated in both the 2% and 4% diet-fed groups at all time intervals. The IgA anti-sheep red blood cell (SRBC) plaque-forming cell (PFC) response generated after oral immunization with SRBC did not differ between the control and the 4% diet group at any time interval, yet the IgA PFC/spleen response was significantly reduced in the 2% diet group at all time intervals studied. However, the IgA PFC/10(6) spleen cells was reduced only with the 2% protein diet group at 6 weeks. Severely protein-deficient mice replenished with the control diet for 3 weeks showed a recovery to values similar to the 8-week control group of both the IgA PFC response and the total IgA concentration in intestinal washes. These results suggest that protein deprivation leads to a reversible reduction in the IgA response to antigens encountered at the intestinal mucosa.