Effect of vitamin A and protein-calorie undernutrition on immune responses.

In rats rendered vitamin A-deficient, there was a marked atrophy of the thymus and the spleen. To a large extent, but not completely, these changes were a result of the concomitant protein-calorie undernutrition. In the thymus the cortex was depleted of lymphocytes. The number of germinal centres was reduced in the spleen. The incorporation of [3H-methyl]thymidine into DNA in cells derived from thymus and spleen of deficient animals was six times lower than in normal littermate controls. On administration of sheep erythrocytes (SRBC), the number of plaque-forming cells per million nucleated spleen cells in deficient animals was 73±6, as compared with 141±36 in normal controls. Similar observations were made on the titres of haemagglutinins and haemolysins formed in response to SRBC. The response of vitamin A plus protein-calorie-deficient animals to diphtheria and tetanus toxoid injection was poorer than the pair-fed controls. These studies demonstrate an important influence of vitamin A and protein-calorie nutrition on lymphoid organs and on immune responses.