Humoral Immune Responses to Pneumocystis jirovecii Antigens in HIV-Infected and Uninfected Young Children with Pneumocystis Pneumonia

Walzer PD (2013) Humoral Immune Responses to Pneumocystis jirovecii Antigens in HIV-Infected and Uninfected Young Children with Pneumocystis Pneumonia. PLoS ONE 8(12): e82783. doi:10.1371/journal.pone.0082783 Humoral Immune Responses to Pneumocystis jirovecii Antigens in HIV-Infected and Uninfected Young Children with Pneumocystis Pneumonia Kpandja Djawe 0 Kieran R. Daly 0 Linda Levin 0 Heather J. Zar 0 Peter D. Walzer 0 Marta Feldmesser, Albert Einstein College of Medicine, United States of America 0 1 Department of Environmental Health, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America, 2 Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America, 3 Research Service, Veterans Affairs Medical Center , Cincinnati , Ohio, United States of America, 4 Department of Pediatrics and Child Health, University of Cape Town , Cape Town , South Africa Background: Humoral immune responses in human immunodeficiency virus (HIV)-infected and uninfected children with Pneumocystis pneumonia (PcP) are poorly understood. Methods: Consecutive children hospitalized with acute pneumonia, tachypnea, and hypoxia in South Africa were investigated for PcP, which was diagnosed by real-time polymerase chain reaction on lower respiratory tract specimens. Serum antibody responses to recombinant fragments of the carboxyl terminus of Pneumocystis jirovecii major surface glycoprotein (MsgC) were analyzed. Results: 149 children were enrolled of whom 96 (64%) were HIV-infected. PcP occurred in 69 (72%) of HIV-infected and 14 (26%) of HIV-uninfected children. HIV-infected children with PcP had significantly decreased IgG antibodies to MsgC compared to HIV-infected patients without PcP, but had similar IgM antibodies. In contrast, HIV-uninfected children with PcP showed no change in IgG antibodies to MsgC, but had significantly increased IgM antibodies compared to HIV-uninfected children without PCP. Age was an independent predictor of high IgG antibodies, whereas PcP was a predictor of low IgG antibodies and high IgM antibodies. IgG and IgM antibody levels to the most closely related MsgC fragments were predictors of survival from PcP. Conclusions: Young HIV-infected children with PcP have significantly impaired humoral immune responses to MsgC, whereas HIV-uninfected children with PcP can develop active humoral immune responses. The children also exhibit a complex relationship between specific host factors and antibody levels to MsgC fragments that may be related to survival from PcP. - Funding: This work was supported by the National Institutes of Health Grant R01 HL090335 and the Department of Veterans Affairs, the National Research Foundation, South Africa; an ASTRA-Zeneca Respiratory Award from the South African Thoracic Society and the Medical Research Council of South Africa. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: ASTRA-Zeneca gave a research grant to the South African Thoracic Society (SATS) and the grant was administered by SATS. ASTRA-Zeneca had nothing how SATS administered the grant or spent the money. ASTRA-Zeneca had nothing to do with any other relevant declarations relating to employment, consultancy, patents, products in development, or marketed products etc). We also confirm that this grant does not alter our adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in our guide for authors. These authors contributed equally to this work. Pneumocystis jirovecii is an opportunistic pulmonary pathogen of worldwide distribution. Primary P. jirovecii infection is acquired during the first few months of life, and is either asymptomatic or a self-limited infection [1,2]. Seroepidemiological studies have shown that by 2-3 years of age, most healthy children have been infected with the organism [2-6]. P. jirovecii remains a major cause of lifethreatening pneumonia (termed PcP) in children who are immunocompromised by human immunodeficiency virus (HIV) infection, cancer, or other disorders. This is especially true in children in low or middle income countries where the disease occurs in 10% to 49% of HIV-infected children hospitalized for pneumonia with an in-hospital mortality rate of 20% to 63% [7-11]. The diagnosis of PcP has traditionally been made by the demonstration of the organism by histologic or immunofluorescent staining in specimens that have been carefully obtained from the respiratory tract. It is likely that this method underestimates the true incidence of PcP, particularly in areas with limited laboratory facilities [1-14]. Recent studies in adults with and without PcP have shown that the polymerase chain reaction (PCR), particularly real time (RT)-PCR, is more sensitive than microscopy in detecting P. jirovecii and may also distinguish colonization from active disease [15-21]. We have obtained similar results with the use of RT-PCR in the diagnosis of PcP and tuberculosis in young children [22-24]. HIV-infected children with PcP have markedly decreased CD4+ cell counts and broad defects in cellular and humoral function, as illustrated by their low serum antibody levels to common infectious agents and to immunizations [25-28]. HIVuninfected children, who are exposed to HIV but remain HIVnegative, have been reported to be at greater risk for developing PcP than HIV-uninfected, unexposed children [29,30]; however, the reasons for the difference are unclear [31-34]. Little is known about the role of specific immune responses to P.jirovecii in HIV-infected children with or without PcP. Over the past decade, the development of recombinant antigens has begun to change this picture. The major surface glycoprotein (Msg) of P.jirovecii plays a central role in the interaction of the organism with the host; contains protective B and T cell epitopes; is encoded by a multi-gene family, and is capable of antigenic variation [35-39]. We have developed 3 recombinant fragments (MsgA, MsgB, MsgC1) that span the length of a single Msg isoform [23], and analyzed their reactivity in both adult and pediatric populations [6,40-48]. MsgC1, which contains the carboxyl terminus and is the most conserved part of Msg, showed the most promise; thus, 3 variants (MsgC3, MsgC8, and MsgC9) were developed to better characterize the reactivity of the antibodies [40-48]. The aims of this study were: 1) to characterize the IgG and IgM antibody responses to MsgC fragments in HIV-infected and HIV-uninfected children hospitalized with PcP (PcP+) and other causes of pneumonia (PcP-); 2) to identify specific host factors that are independent predictors of these antibody levels; 3) to determine if any of the antibody responses are independent predictors of mortality from PcP. Materials and Methods Study Design A prospective study was conducted of consecutive children adm (...truncated)