EFFECT OF RADIOTHERAPY ON THE LEVELS OF SECRETORY IMMUNOGLOBULIN-A AGAINST INDIGENOUS AND VIRULENT STREPTOCOCCI

It is well known that the frequency of upper respiratory infection is clinically increased after radiotherapy of the head and neck region. T his study found higher antibacterial secretory immunoglobuin A (S-IgA) activity against three indigenous streptococci (Streptococcus mitis, S. salivarius, and S. sanguis I) and S. pneumoniae in patients who had undergone radiation therapy of the head and neck region than in contr ol subjects. This showed no relation to the extent of the radiation fi eld. Compared with before radiotherapy the S-lgA titer against S. pneu moniae and its ratio to the activities against the indigenous streptoc occi were significantly higher in patients with fully irradiated major salivary glands. These results indicated that the radiotherapy promot ed the antigen-specific S-lgA production of virulent streptococci in m ost patients with head and neck cancer, even more than 6 months after radiotherapy. The resulting altered balance in the S-IgA system of nor mal indigenous streptococci may also impair the ability to maintain th e stable bacterial interference between normal indigenous and virulent streptococci in the oropharyngeal cavity.