37 cantly in older people. Alpha and beta globulin levels tended to show someincrease though the correlation with age wasnot significant. Albumin levels tended to decrease slightly in older people. Pronounced differences in serum protein levels were noted in theexposed population. The albumen levels were significantly higher and the globulin levels significantly lower than in the unexposed group. Alpha 1, alpha 2, and gammaglobulins showed the most pronounced depression in the exposed group (Table 16). Serum proteins, particularly gamma globulins, showed greatest defi- lesions, and intestinal parasites. Thereforeit is not surprising that they have elevated gammaglobulin levels. The A/G ratio is reduced or reversed in most of the people. The serum protein levels are generally elevated, which mayin part be related to dehydration associated with a tropical environment where dependencefor water is on rainfall which is scant at certain seasons. The specific gravity of the urine is frequently high, and reduced red cell and blood volume have been found. In spite of these factors the present studies should provide valid comparisons of the exposed and un- Theresults of the immunodiffusion studies are exposed Marshallese populations, since both groups are generally exposed to the same environmental the increase in serum gammaglobulin levels, the acteristics show them to be a relative homogenous cits in the older exposed age groups. shown in Table 16 and in Figure 37. Parallel to immunoglobulins showedincreasing values in the older age groups of the unexposed people. The in- crease in IgG moiety was most pronounced and showedsignificant correlation with age (r =0.78). The increase in the other immunoglobulins did not show a high correlation with age. The increase in the K light chains was highly correlated with age (7 =0.96). Higher K/L ratios were noted in the older people though there wasnosignificant correlation with age (r=0.41). In the exposed population all the immunoglobulins were depressed below levels of the unexposed group, the most pronounced depression being in the IgG and IgA moieties and in the L light chains. Discussion Thoughthe role of immune mechanismsin the aging process has never been clearly defined, it is generally agreed that such mechanismsare impaired in senescence. Ram*® pointed out that “... itis well established that the capacity for immune responses increases during neonatal and juvenile life to a maximum in the young adult animal, it remains constantfor a time and then gradually decreases as the animal ages.” The results of the present studies in the Marshallese people seem generally to supportthis thesis. In connection with the results of these studies, it should be pointed out that the Marshallese people understudyare notstrictly comparable with a population in the United States because of certain environmental andracial differences. As is generally true throughout Micronesia, even thoughliving standards have been improving, the people are subject to frequent infections such as gastroenteritis, upper respiratory infections, skin factors, and studies of genetically inherited char- population. These studies are believed to test the immunological status of the individuals to some degree. althoughinterpretation of some of the results is not readily apparent. Theresults of the various tests for the unexposed population are discussed below in termsof correlation with aging. Thedifferences in the results for the exposed population are then discussed with regard to radiation-induced effects. In the unexposed comparison population itis obvious from the various graphsthat, even in the tests showing changes moreclosely correlated with aging, the changes are maximum bythe middle years (usually in the 40 to 50 age group) withlittle or no increase, or in somecases even slight reduction. after middle age. Thereasonfor this is not apparent. The response of lymphocytes to PHA stimula- tion in peripheral blood cultures wastested because of the active role of the lymphocyte in maintaining immunological integrity. PHA is gen- erally believed to evoke a nonspecific blastogenic response in such cultures, since many more lymphocytes are transformed andproliferate with this agent than with specific antigens (such as tuberculin, tetanus, thyroid, pertussis, etc.). It is controversial whether or not PHAinthis situation induces antibody formation. The exact mechanism of action of the mitogen is unknown. Conard and Demoise,*? using autoradiographic and subcellular fractionation techniques, showed thata tritiated PHAwaslocalized largely in the cytoplasm of transformed lymphocytes, with the greatest concentration in the mitochondrial fraction, which suggested that such organelles may be involved in initiation of lymphocyte transformation.