Sulfa resistance in mouse-derived Pneumocystis carinii

Pneumocystis jirovecii dihydropteroate synthase gene mutations in a group of HIV-negative immunocompromised patients with Pneumocystis pneumonia

The purpose of this study was to investigate dihydropteroate synthase (DHPS) mutations and their clinical context in non-HIV-infected patients with Pneumocystis pneumonia (PCP). DHPS genes in respiratory samples collected from HIV-negative patients with PCP presented between January 2008 and April 2011 were amplified by polymerase chain reaction (PCR) and sequenced. Basic clinical data from the medical records of the patients were also reviewed. The most common point mutations, which result in Thr55Ala and Pro57Ser amino acid substitutions, were not detected in the Pneumocystis jirovecii sampled from the HIV-negative patients. Two other point mutations, which result in nonsynonymous mutation, Asp90Asn and Glu98Lys, were identified in P. jirovecii from two patients. Among the patients, the levels of lactate dehydrogenase (LDH), C-reactive protein (CRP) and plasma (1-3) β-D-glucan were elevated in 75, 92.31 and 42.86% of patients, respectively. The percentage of circulating lymphocytes was significantly lower in non-survivors than in survivors [4.2%, interquartile range (IQR) 2.4-5.85 versus 10.1%, IQR 5.65-23.4; P=0.019]. The neutrophil proportion in bronchoalveolar lavage fluid (BALF) was significantly higher in non-survivors than in survivors (49.78±27.67 versus 21.33±15.03%; P=0.047). Thirteen patients had received adjunctive corticosteroids (1 mg/kg/day prednisone equivalent) and nine (69.23%) of them eventually experienced treatment failure. No common DHPS gene mutations of P. jirovecii were detected in the HIV-negative PCP patients. However, other mutations did exist, the significance of which remains to be further identified. The elevation of neutrophil counts in BALF and reduction of the number of lymphocytes in peripheral blood may be associated with poor outcome. The efficacy of adjunctive steroid therapy in HIV-negative patients with P. jirovecii infection requires further investigation.

Drug resistance in Pneumocystis carinii: an emerging problem

Pneumocystis carinii pneumonia (PCP) is a frequent opportunistic infection in AIDS patients. Large numbers of HIV-infected individuals take prophylactic medications to prevent this illness. The development of drug resistance, while expected, cannot be monitored by classical means, since the organism cannot be cultivated in vitro. Two drug target genes, dihydropteroate synthase (DHPS) and cytochrome b, have been cloned and sequenced from human-derived P. carinii. Mutations leading to amino acid substitutions in the active sites of both proteins have been detected in patients receiving prophylaxis with sulfonamides and sulfones (DHPS inhibitors) and with atovaquone (cytochrome b inhibitor), suggesting that drug resistance may indeed be developing.

Prophylaxis failure is associated with a specific Pneumocystis carinii genotype

To investigate the possible association between Pneumocystis carinii types and various clinical and demographic parameters, we used molecular typing to analyze 93 bronchoalveolar lavage specimens from patients with P. carinii pneumonia (PCP). Multivariate regression analysis revealed an association between being infected with a specific P. carinii genotype and receiving anti-PCP prophylaxis (odds ratio, 4.4; 95% confidence interval, 1.0-18.6; P=.05), although no association with a specific drug was detected.

Immunization with recombinant Pneumocystis carinii p55 antigen provides partial protection against infection: characterization of epitope recognition associated with immunization

Many therapeutic options exist for the treatment of Pneumocystis carinii pneumonia, a common fungal opportunistic pulmonary pathogen, but treatment is often complicated by side effects and toxicity and, more recently, markers of drug resistance have been described. The development of immunotherapetic modalities such as active immunization or passive immunotherapy may play an increasing important role in the prevention and treatment of infection. Passive immunotherapy with polyclonal anti-P. carinii reagents, such as serum or T cells, and monospecific reagents reactive with the major surface glycoprotein (MSG or gpA), such as monoclonal antibodies or MSG primed T cells, reduce the severity or eradicate infection. Active immunization with whole P. carinii, P. carinii extracts or MSG has afforded partial protection against the subsequent development of P. carinii pneumonia in some animal models. Identification of additional antigens with protective benefits will aid in the development of vaccines or other reagents. The p55 antigen of rat-derived P. carinii is well recognized by animals following natural exposure to the organism. This 414 amino acid residue antigen found within the cell wall of P. carinii contains 7 repeats of a glutamic acid-rich motif in the carboxyl portion of the molecule. Both humoral and cellular immune responses reactive with this repeated domain are present following natural infection while, the amino terminal portion of the molecule is immunologically silent. In this study, immunization with recombinant p55 elicited significant humoral and cellular immune responses which persisted during 10 weeks of immunosupression in corticosteroid treated rats; rp55 immunization resulted in a significant reduction in organism burden, improved histological score, lower lung weight to body weight ratio (a marker of infection or lung inflammation) and improved survival (P < 0.01). Greater protection was afforded by immunization with a peptide containing amino acid residues 1-200, than by the entire rp55 molecule. Epitope recognition by serum from animals immunized with rp55 differed from that of naturally exposed animals with oligoclonal responses to residues 22-92 and residues 196-218. This study demonstrates that protection against P. carinii can be afforded by immunization with antigen preparations other than whole extracts of P. carinii or the major surface antigen, MSG. This antigen moiety will likely be most useful as a vaccine candidate in combination with other immunogens which provide similar partial protection.