Proteins (66 kD and 43 kD) were coincidentally purified with hsp70 (Fig. patients with low titres ( 1:4) had detectable levels of anti-hsp70 antibody. Sera Metformin HCl from patients positive for anti-hsp70 antibody showed high titres in the Eiken latex agglutination test for the detection of serum cryptococcal antigen. Our results indicate that this 70-kD hsp family fromC. neoformansappears to be a major target molecule of the humoral response, not Metformin HCl only in murine pulmonary cryptococcosis, but also in human patients with pulmonary cryptococcosis. Keywords:anti-C. neoformanshsp70 antibody,C. neoformans, pulmonary cryptococcosis == INTRODUCTION == Hsp or stress proteins are synthesized by all cells in response to various types of environmental stress and probably function as molecular chaperones in normal physiological processes. In recent years it has been observed that members of the hsp family, including hsp70 from several pathogenic microbes, are antigenic. Moreover, hsp of an invading microbe are often immunodominant targets of cellular and humoral immune responses [1]. This is particularly true for members of the hsp70 family, which are among the most immunogenic proteins of pathogenic microorganisms [2]. For instance, hsp70s are thought to play an important role in infections caused byPlasmodium[3],Trypanosoma[4],Schistosoma[5],Leishmania[6], andMycobacterium[7] species. In the field of fungal pathogens, a Metformin HCl member of the hsp70 family ofHistoplasma capsulatumwas recognized as a target of cell-mediated, protective immunity [8] and the hsp70 family ofCandida albicansappears to be expressed as both B cell Metformin HCl and T cell immunogens in human subjects, with a possible important role in infections caused byC. albicans[9]. Further, the microbial hsp are the antigens of choice for vaccines in various infectious diseases. Several studies have suggested the potential usefulness of microbial hsp as a candidate for the design of subunit vaccines, e.g. hsp90 in candidiasis [10], hsp60 in histoplasmosis [11], and hsp70 in schistosomiasis [12]. The fungusCryptococcus neoformansis primarily a pathogen for individuals with impaired cell-mediated immunity. Contamination withC. neoformansis a major problem in HIV-infected individuals; in New York City, 68% of patients with AIDS develop cryptococcal meningitis [13]. There is also an increased prevalence of cryptococcosis in patients receiving therapeutic doses of corticosteroids, patients with lymphoreticular malignancies (especially Hodgkin’s disease), those with a renal transplantation, and with sarcoidosis (even in the absence of corticosteroid therapy). Diabetes mellitus has also been cited as a predisposing factor for cryptococcosis. However, patients with cryptococcosis but without any underlying disease may also sometimes report at health clinics. Several studies have shown the importance of T lymphocytes, CD4+and CD8+, in mediating pulmonary clearance ofC. neoformansin mice [14]. B cell-deficient mice are not at increased risk of Cryptococcal infection [15]. However, the presence of antibodies, acting as potent opsonins [16] required for natural killer cell [17] and leucocyte [18] anti-fungal activityin vitrosuggests that humoral immunity plays an important role in this infection. Recently, there has been renewed interest in antibody immunity to glucuronoxylomannan (GXM) for prevention [19] and treatment [20] of human infection. To date, some studies ofC. neoformansprotein have been described [2123]. However, little is known about the proteins secreted or released byC. neoformans, despite evidence that they elicit important immune responses. We recently analysed the serological responses of mice with pulmonary cryptococcosis [24]. Briefly, Western blotting analysis showed that experimentally induced pulmonary cryptococcosis in (BALB/c DBA/2)F1mice was associated with the appearance of serum antibodies to a 77-kD protein derived fromC. neoformansas well as to 18-, 22-, 25-, 36- and 94-kD proteins. The immunodominant 77-kD band also reacted with antibodies against hsp70 family members. Further, we CXADR purified a 77-kD antigen fromC. neoformanscell extracts. N-terminal amino acid sequencing of the 77-kD antigen confirmed that it was a member of the hsp70 protein family. These results showed that the 70-kD hsp family fromC. neoformanswas the major target molecule of the humoral response in murine pulmonary cryptococcosis. To our knowledge, this was the first report of hsp fromC. neoformans. In the present study, we examined the antibody response in the sera of 21 patients with proven pulmonary cryptococcosis and three patients with suspected disease, and compared these responses with those in patients with other pulmonary diseases and deep mycoses. == PATIENTS AND METHODS == == Subjects == == Patients with pulmonary cryptococcosis == Serum samples were collected from 21 patients with pulmonary cryptococcosis admitted to the.