Periodontal Bone Loss and Immune Characteristics of Congenitally Athymic and Thymus Cell-reconstituted Athymic Rats

We investigated the ability to reconstitute the T-cell deficiency in congenitally athymic (nude; rnu/rnu) Rowett rats by intravenous injection of 10(7) heterozygous normal (rnu/+) rat thymus cells. The thymus cell-reconstituted animals showed essentially normal lymphocyte proliferation to phytohemagglutinin P and concanavalin A, normal spleen and lymph node T-lymphocyte distribution, and normal serum immunoglobulin G levels. These rats were used to study the effect of T-cell deficiency on periodontal disease. Animals with minimal oral flora were divided into three groups: nude, thymus cell-reconstituted nude, and normal rats. Immune response, gingival inflammation, and periodontal bone loss were examined in these animals. Less than 40% of the T cells recovered from the normal rat gingiva could be recovered from the nude rat gingiva. In contrast to the situation in normal or thymus cell-reconstituted rat gingiva, B cells were vastly predominant in the nude rat gingiva, with approximately four B cells for each T cell. There was increased periodontal bone loss in the nude rats compared with that in the normal rats. Thymus cell reconstitution of the nude rats was associated with decreased bone destruction. It is suggested that T cells have a regulatory function in relation to the potentially excessive B-cell response to abundant antigen and polyclonal activators in the oral cavity.