B cell and antibody responses in mice induced by a putative cell surface peptidase of Pneumocystis murina protect against experimental infection

Abstract

Rationale Pneumocystis pneumonia is a major cause of morbidity and mortality in HIV-infected subjects, cancer patients undergoing chemotherapy and solid organ transplant recipients. No vaccine is currently available. By chemical labeling coupled with proteomic approach, we have identified a putative surface protein (SPD1, Broad Institute gene accession number PNEG_01848) derived from single suspended P. murina cysts. SPD1 was expressed in an insect cell line and tested for vaccine development. Methods Mice were immunized with SPD1 plus adjuvant MF-59 by subcutaneous injection. Three weeks after the last immunization, CD4+ cells were depleted with anti-CD4 antibody GK1.5. The mice were then challenged with 2 × 105 Pneumocystis organisms. Mice were sacrificed at 4 and 6 weeks after PC challenge. Spleen/lung cells and serum were harvested. B cells and memory B cells were assessed via flow cytometry. Specific Pneumocystis IgG antibody was measured by ELISA before and after challenge. Infection burden was measured as real-time PCR for P. murina rRNA. Results Normal mice infected with Pneumocystis mounted a serum IgG antibody response to SPD1. Serum from rhesus macaques exposed to Pneumocystis showed a similar serum IgG response to purified SPD1. SPD1 immunization increased B cell and memory B cell absolute cell counts in CD4-depleted Balb/c mice post Pneumocystis challenge in spleen and lung. Immunization with SPD1 significantly increased specific Pneumocystis IgG antibody production before and after challenge. Mice immunized with SPD1 showed significantly decreased P. murina copy number compared with mice that did not receive SPD1 at 6 weeks after challenge. Conclusion Immunization with SPD1 provides protective efficacy against P. murina infection. SPD1 protection against Pneumocystis challenge is associated with enhanced memory B cell production and higher anti–Pneumocystis IgG antibody production. SPD1 is a potential vaccine candidate to prevent or treat pulmonary infection with Pneumocystis.

Deceleration of glycometabolism impedes IgG‐producing B‐cell‐mediated tumor elimination by targeting SATB1

“…Since their discovery in the mid‐1960s, B lymphocytes were mainly known for their ability to produce antibodies . The B‐cell‐derived antibody response has been reported to be critical to protect against microbial infections or mediate autoimmune diseases . Although the role of B cells in tumors is still conflicting and controversial, due to their antibody‐producing capacity, tumor‐infiltrating B cells are recognized as anti‐tumor immune components …”

CD4+T Cell Regulation of Antibodies Cross-Reactive with Fungal Cell Wall-Associated Carbohydrates afterPneumocystis murinaInfection

“…H ost defense against the opportunistic pulmonary fungal pathogen Pneumocystis jirovecii involves the interplay between innate and adaptive immune responses, ultimately initiated through the recognition of specific Pneumocystis antigens. Currently, few Pneumocystis protein antigens have been identified as capable of initiating adaptive host defense responses with good protective benefit in models of infection (1)(2)(3)(4). Several Pneumocystis protein antigens demonstrate significant diversity between the different host-restricted Pneumocystis species or are generated from multicopy gene families, hindering the assessment of potential vaccine candidates for protection against human disease (5).…”

Overcoming Hurdles to Development of a Vaccine against Pneumocystis jirovecii

“…There is currently no reliable system for maintaining organisms in long-term culture, so understanding the genetics of Pneumocystis has been very difficult and slow going. Ruan et al recently used a chemical labeling and proteomic approach to identify a putative surface protein from P. murina named SPD1 (22). Vaccination with the C-terminal portion of SPD1 resulted in antibody responses that corresponded with significant reduction in Pneumocystis lung burden in CD4 T cell-depleted mice (22).…”

“…Ruan et al recently used a chemical labeling and proteomic approach to identify a putative surface protein from P. murina named SPD1 (22). Vaccination with the C-terminal portion of SPD1 resulted in antibody responses that corresponded with significant reduction in Pneumocystis lung burden in CD4 T cell-depleted mice (22). Serum antibody from SIV/HIV-infected rhesus macaques exposed to Pneumocystis recognized SPD1 (22).…”

“…Vaccination with the C-terminal portion of SPD1 resulted in antibody responses that corresponded with significant reduction in Pneumocystis lung burden in CD4 T cell-depleted mice (22). Serum antibody from SIV/HIV-infected rhesus macaques exposed to Pneumocystis recognized SPD1 (22). Identification of surface proteins using proteomic approaches will undoubtedly lead to identification of more vaccine candidates (23).…”