Serologic responses to pneumocystis proteins in HIV patients with and without Pneumocystis jirovecii pneumonia

J Acquir Immune Defic Syndr. 2011 Jul 1;57(3):190-6. doi: 10.1097/QAI.0b013e3182167516.


Background: Immune responses to Pneumocystis jirovecii are not well understood in HIV infection, but antibody responses to proteins may be useful as a marker of Pneumocystis risk or presence of Pneumocystis pneumonia (PcP).

Design: Retrospective analysis of a prospective cohort.

Methods: Enzyme-linked immunosorbent assays of antibodies to recombinant Pneumocystis proteins of major surface glycoprotein fragments (MsgC1, C3, C8, and C9) and of antibody titers to recombinant kexin protein (KEX1) were performed on 3 sequential serum samples up to 18 months before and 3 samples after first AIDS-defining illness from Multicenter AIDS Cohort Study participants and compared between those who had PcP or a non-PcP AIDS-defining illness.

Results: Fifty-four participants had PcP and 47 had a non-PcP AIDS-defining illness. IgG levels to MsgC fragments were similar between groups before first AIDS-defining illness, but the PcP group had higher levels of IgG to MsgC9 (median units/mL 50.2 vs. 22.2, P = 0.047) post-illness. Participants with PcP were more likely to have an increase in MsgC3 [odds ratio (OR): 3.9, P = 0.02], MsgC8 (OR: 5.5, P = 0.001), and MsgC9 (OR: 4.0, P = 0.007). The PcP group was more likely to have low KEX1 IgG before development of PcP (OR: 3.6, P = 0.048) independent of CD4 cell count and to have an increase in high IgG titers to KEX1 after PcP.

Conclusions: HIV-infected individuals develop immune responses to both Msg and kexin proteins after PcP. Low KEX1 IgG titers may be a novel marker of future PcP risk before CD4 cell count has declined below 200 cells per microliter.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • AIDS-Related Opportunistic Infections / blood
  • AIDS-Related Opportunistic Infections / immunology
  • Adult
  • Antibodies, Fungal / blood*
  • Biomarkers
  • Enzyme-Linked Immunosorbent Assay / methods
  • Fungal Proteins / immunology*
  • HIV Infections / complications*
  • Humans
  • Immunoglobulin G / blood
  • Immunoglobulin M / blood
  • Membrane Glycoproteins / immunology
  • Middle Aged
  • Pneumocystis carinii / immunology*
  • Pneumonia, Pneumocystis / blood
  • Pneumonia, Pneumocystis / immunology*
  • Risk Factors
  • Serine Endopeptidases / immunology


  • Antibodies, Fungal
  • Biomarkers
  • Fungal Proteins
  • Immunoglobulin G
  • Immunoglobulin M
  • Membrane Glycoproteins
  • GPA protein, Pneumocystis carinii sp.
  • Kex1 protein, Pneumocystis jirovecii
  • Serine Endopeptidases