Serologic Responses to Recombinant Pneumocystis jirovecii Major Surface Glycoprotein among Ugandan Patients with Respiratory Symptoms

Abstract

BackgroundLittle is known about the serologic responses to Pneumocystis jirovecii major surface glycoprotein (Msg) antigen in African cohorts, or the IgM responses to Msg in HIV-positive and HIV-negative persons with respiratory symptoms.MethodsWe conducted a prospective study of 550 patients, both HIV-positive (n = 467) and HIV-negative (n = 83), hospitalized with cough ≥2 weeks in Kampala, Uganda, to evaluate the association between HIV status, CD4 cell count, and other clinical predictors and antibody responses to P. jirovecii. We utilized ELISA to measure the IgM and IgG serologic responses to three overlapping recombinant fragments that span the P. jirovecii major surface glycoprotein: MsgA (amino terminus), MsgB (middle portion) and MsgC1 (carboxyl terminus), and to three variations of MsgC1 (MsgC3, MsgC8 and MsgC9).ResultsHIV-positive patients demonstrated significantly lower IgM antibody responses to MsgC1, MsgC3, MsgC8 and MsgC9 compared to HIV-negative patients. We found the same pattern of low IgM antibody responses to MsgC1, MsgC3, MsgC8 and MsgC9 among HIV-positive patients with a CD4 cell count <200 cells/µl compared to those with a CD4 cell count ≥200 cells/µl. HIV-positive patients on PCP prophylaxis had significantly lower IgM responses to MsgC3 and MsgC9, and lower IgG responses to MsgA, MsgC1, MsgC3, and MsgC8. In contrast, cigarette smoking was associated with increased IgM antibody responses to MsgC1 and MsgC3 but was not associated with IgG responses. We evaluated IgM and IgG as predictors of mortality. Lower IgM responses to MsgC3 and MsgC8 were both associated with increased in-hospital mortality.ConclusionsHIV infection and degree of immunosuppression are associated with reduced IgM responses to Msg. In addition, low IgM responses to MsgC3 and MsgC8 are associated with increased mortality.

Serological diagnosis of pneumocystosis: production of a synthetic recombinant antigen for immunodetection of Pneumocystis jirovecii

“…In the state of art of serological diagnosis of PcP, different authors have studied the immune response of patients with and without PcP with different fractions of the recombinant protein Msg of P. jirovecii 1617181920212223242526. Although there are an estimated 100 related but unique copies of the MSG gene in the Pneumocystis genome, a greater variability is notice in the amino-terminus of the Msg protein and the most conserved sequences are present at the carboxyl-terminus.…”

“…Alternatively, promising studies using recombinant antigens of P. jirovecii and antibody immunodetection techniques, such as immunoenzymatic or immunoblotting assays, have shown potential application in the diagnosis and epidemiological studies of PcP1617181920212223242526. The Pneumocystis antigen that has received the most attention is the major surface glycoprotein (Msg), which contains shared and species-specific epitopes, elicits humoral and cellular protective immune responses and plays a central role in the interaction of Pneumocystis with its host27.…”

“…The Pneumocystis antigen that has received the most attention is the major surface glycoprotein (Msg), which contains shared and species-specific epitopes, elicits humoral and cellular protective immune responses and plays a central role in the interaction of Pneumocystis with its host27. The carboxyl-terminal domain of the Msg is reported to be highly immunogenic, the most conserved and reactive region of Msg and to contain both B and T cell conserved protective epitopes1618232425. Therefore, recombinant synthetic amino acid sequences, designed to hold more than one reactive region of the Msg, are promising tools that can increase the sensitivity, specificity, the cost-effectiveness and the standardization of serological tests28.…”

A Molecular Window into the Biology and Epidemiology of Pneumocystis spp

“…It has long been hypothesized that this subfamily plays a critical role in pathogen-host interactions, including adhesion to host cells and extracellular matrix proteins (261)(262)(263)(264), evasion of host immune attacks via antigenic variation (237,(265)(266)(267)(268), and masking of immune activation by ␤-glucans (216). Evidence in support of their role in antigenic variation includes the preservation of all required components of the DNA recombination machinery (69), the clustering of msg genes almost exclusively in subtelomeric regions to facilitate recombination (69,242), the presence of strong serological responses to Msg proteins in patients with PCP (30,(269)(270)(271), the selective expression of Msg variants among different organisms in the same infected lung (267), and the occurrence of discordant antibody and cellular responses to Msg variants in animal models (268). The last observation suggests that antigenic variation may target T-cell responses, not antibody responses.…”

Recent Advances in the Diagnosis of <I>Pneumocystis</I> Pneumonia

“…Msg fragments at the C-terminus were recognized more frequently by serum specimens than those at the N-terminus 29,30) . HIV-infected patients with PCP elicited greater responses against MsgC than did HIV-infected patients without PCP or with pneumonia due to other causes, and a prior episode of PCP also presented a higher titer of antibodies against MsgC fragments 27,31) .…”