The aim of this retrospective study is to evaluate the correlation between T-cell immunity and pulmonary disorders in a group of Italian subjects with HIV infection. HIV-infected patients seen at the Institute of Infectious Diseases, University of Verona, were included in this study if they had a specific acute pneumonia, a CD4+ cell count and a CD4+/CD8+ ratio during the 60 days immediately before the onset of pulmonary disease. Cases receiving any antimicrobial prophylaxis were excluded. Pneumonia was recognized by usual clinical and radiologic abnormalities. The diagnostic procedure included sputum examination, bronchoscopy with bronchoalveolar lavage and transbronchial biopsy. The specimens were processed for bacterial, mycobacterial and fungal stains and cultures. Ziehl-Neelsen, periodic acid-Schiff and silver methenamine stains were performed on the transbronchial biopsy specimens in addition to usual pathologic examinations mononuclear. Determination of percentage of peripheral blood mononuclear cells bearing CD4+ and CD8+ markers was done by conventional fluorescent antibody cell-sorter analysis of the mononuclear cell population. Absolute number of CD4+ lymphocytes was determined by multiplying the total lymphocyte count by the percent of mononuclear cells bearing CD4+ marker. From October 1987 to August 1991, 61 patients, 50 males and 11 females, had 65 episodes of specific pneumonia. The average age of patients was 31.4 years (range 29-59 years). The risk factors for HIV infection included intravenous drug abuse (47 patients), homosexuality (6 patients), bisexuality (3 patients) and heterosexual contact (5 patients). Before the onset of pulmonary disorders, patients were classified in the following clinical HIV-related stages: asymptomatic state (22 episodes), ARC (22 episodes) and AIDS (21 episodes). In decreasing order of frequency diagnosis of pneumonias were PCP (29 episodes), community-acquired bacterial pneumonia (16 episodes), pulmonary tuberculosis (8 episodes), nonspecific interstitial pneumonia (4 episodes), PCP and pulmonary tuberculosis (3 episodes), cytomegalovirus pneumonia (2 episodes), and one of each episode of PCP and pulmonary cryptococcosis, pulmonary candidiasis, pulmonary Kaposi's sarcoma. The mean and the standard deviation of immunologic values regarding the four primary diagnostic groups were: PCP CD4+/CD8+ 0.50 +/- 0.42, CD4+/mm3 196 +/- 190; bacterial pneumonia CD4+/CD8+ 0.53 +/- 0.44, CD4+/mm3 247 +/- 139; pulmonary tuberculosis CD4+/CD8+ 0.62 +/- 0.38, CD4+/mm3 260 +/- 170; nonspecific interstitial pneumonia CD4+/CD8 + 0.57 +/- 0.48, CD4+/mm3 240 +/- 189. No significant statistical differences with respect to CD4+/CD8 ratios and CD4+ cell counts among these diagnostic groups were found by standard analysis of variance.(ABSTRACT TRUNCATED AT 400 WORDS)