Alveolar bone destruction in the immunosuppressed rat

The placement of a ligature around the second maxillary molar of the conventional rat caused osteoclastic bone resorption and simultaneously, alveolar bone formation. The number of peripheral mononuclear cells in the blood and lymphoblastic transformation of spleen cells in response to concanavalin A increased. Cyclophosphamide (CY), an immunosuppressive agent, given shortly after placing the ligature suppressed the lymphoid reactions, spleen size, and bone formation and enhanced bone destruction. CY given in higher doses also suppressed the number of PMN cells. Septicemia developed in several of these animals. Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli were isolated from the blood and/or ligature. Antibiotics prevented bone destruction. Without placing a ligature, the high dose of CY did not result in bone loss. These findings suggest that 1) bone destruction of the ligature‐treated rat is of bacterial origin, 2) CY suppresses proliferation of osteoblasts but does not seem to interfere with the activity of osteoclasts, and 3) suppression of the host defenses greatly facilitates bone destruction.