Pulmonary infections with Pneumocystis carinfi are an important cause of morbidity and mortality in patients with AIDS. P. carinii infections are seen in patients with decreased numbers of helper T lymphocytes, suggesting that these cells are important in preventing infection. To test this hypothesis, we sought to establish experimental infection with P. carinfi in mice selectively depleted of helper T lymphocytes. Weekly injections of a monoclonal anti-CD4 antibody produced sustained depletion of helper T lymphocytes from blood and lymphoid organs. To establish pulmonary infection, lymphocytedepleted mice were then given intratracheal inoculations of P. carinji organisms derived from the lungs of chronically infected athymic mice. Pulmonary infection with P. carinli was demonstrable in the antibody-treated mice and was centered around the conducting airways. Infection was persistent for up to 3 mo with continued antibody treatments, and yet could be cleared from the lungs if antibody treatments were discontinued. This experimental model of P. carinji infection permits

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FNAB under US guidance is a useful diagnostic modality in the evaluation of thyroid nodules in selected patients with MNG. Because the risk of thyroid malignancy in these nodules is comparable to that which exists in solitary thyroid nodules, the possibility of thyroid malignancy should be considered in all patients with MNG.

Forty patients with the acquired immunodeficiency syndrome (AIDS) and their first episodes of Pneumocystis carinii pneumonia were assigned at random to receive either trimethoprim-sulfamethoxazole or pentamidine isethionate. The two groups did not differ significantly in the severity of pulmonary or systemic processes at enrollment. Five patients treated initially with trimethoprim-sulfamethoxazole and one patient treated initially with pentamidine died during the 21-day treatment period (p = 0.09, Fisher's exact test). No significant differences were seen between groups in rates of improvement, pulmonary function tests, or 67Ga uptake by the lungs in the survivors at completion of therapy. Adverse reactions necessitated changing from the initial drug in 10 patients in the trimethoprim-sulfamethoxazole group and 11 in the pentamidine group. Minor reactions occurred in all patients. In patients with AIDS, trimethoprim-sulfamethoxazole and pentamidine do not have statistically significant differences in efficacy or frequency of adverse reactions.

Published and unpublished data on the cultivation of P. carinii were reviewed by a panel of investigators convened by the National Institutes of Health. Although several cell culture systems allow propagation of P. carinii for a limited time with modest rates of replication, these have not proved adequate for isolation of P. carinii in sufficient quantity to explore important basic biological investigation. Attempts at cell-free culture have yielded only transient proliferation. Because much of the unsuccessful work on cultivation of the organism has been unpublished, the panel agreed that these data may be useful to other investigators in designing experimental strategies for cultivation. Therefore, the purpose of this report is to make available this information to researchers, lest others unknowingly repeat unsuccessful methods. It is hoped that by documenting the history and the complexities of Pneumocystis culture, renewed interest and efforts will be directed toward this fundamental scientific challenge.