The metabolism of different immunoglobulin classes in irradiated mice. IV. Fate of circulating IgA of tumour or transfusion origin.

BALB/c conventional mice carrying plasma cell tumour grafts which secrete IgA do not, in contrast to normal mice, experience any decline in their serum IgA levels following wholebody irradiation by 900 R, provided the tumours themselves are protected from X-ray damage. Germ-free Swiss mice whose serum IgA levels had been raised to near-normal values by a transfusion with normal mouse serum, did not show any selective decline in the serum IgA concentration following whole-body-exposure to 2000 R, in contrast to conventional adult mice in which this class of immunoglobulin is severely and selectively depressed by a similar treatment. Nor did germ-free transfused mice excrete abnormally high quantities of IgA into their intestinal fluids. It is concluded that the previously described selective fall in serum IgA levels following irradiation does not occur when the source supplying IgA to the serum pool is protected from the action of X-rays. Conversely, this metabolic disturbance cannot be explained by any specific increase of catabolism or intestinal loss of this serum immunoglobulin.