Natural killer (NK) cell activity in murine muscular dystrophy. II. Age-related tissue distribution and enhanced NK activity in the thymus of dystrophic mice.

The age-related tissue distribution of natural killer (NK) cell activity in murine muscular dystrophy was investigated. Lymphoid tissues including the spleen, thymus, mediastinal (or bronchial) lymph nodes (BLN), mesenteric lymph nodes (MLN), inguinal/popliteal lymph nodes (PLN1), and axillary/brachial lymph nodes (PLN2) were obtained from various aged normal (+/+) and dystrophic (dy2J/dy2J) C57BL/6J mice. Cell suspensions were incubated with 51Cr-labeled YAC-1 lymphoma target cells in a 4-hr 51Cr-release assay. The data indicated that dystrophic mice, at all ages studied, had elevated levels of NK activity in the spleen, BLN, MLN, PLN1, and PLN2 as compared with the normal age- and sex-matched control group. The NK activity in the thymocyte population from dystrophic mice at 2 weeks of age was found to be negligible, while at 8 weeks of age it was two-fold higher than that for the normal control group. In addition, dystrophic mice had an age-related decline in NK activity in all tissues after 10 weeks of age but the activity was still elevated at 40 weeks of age as compared with the normal control group. Target cell binding studies revealed that the number of conjugate-forming cells in thymocytes from 8-week-old dystrophic mice were found to be significantly higher than that found in normal mouse thymocytes using NK-sensitive YAC-1 tumor target cells. The number of cells bound per YAC-1 target cell ranged from 1 to 3 for dystrophic mouse thymocytes as compared with 1 to 2 for the normal control group. Thus, the data indicate an elevated NK activity in all lymphoid tissues studied from dystrophic mice of different ages. In addition, the thymus from dystrophic mice at 8 weeks of age contains an enhanced number of conjugate-forming NK cells and NK activity.