Stimulation of human B lymphocytes by Nocardia-delipidated cell mitogen and derived fractions from N. opaca. Structure-activity relationship.

Nocardia-delipidated cell mitogen (NDCM), a particulate fraction prepared from Nocardia opaca, is able to stimulate the proliferation of small resting human B lymphocytes and their differentiation into Ig-secreting cells. This fraction contains two active structures: the cell wall peptidoglycan (PG) and a fraction (Cy I) derived from the cytoplasmic compartment. Treatment of insoluble PG with various bacteriolytic enzymes showed that the minimal structure required for mitogenic activity is more complex than that required for the differentiation of human lymphocytes. The mitogenic activity of cell wall fractions varies in different bacterial species; that prepared from N. opaca is the more potent. Both mitogenic structures of N. opaca induce higher responses in infant and adult PBL as compared to cord lymphocytes. The differentiation of B lymphocytes into Ig-secreting cells induced by PG fractions is T-dependent.