title: Role of signal sequence in vaccine-induced protection against experimental coccidioidomycosis.
abstract: The vaccine efficacy of the gene sequence encoding the signal peptide of the antigen known as antigen 2 or proline-rich antigen (Ag2/PRA), an immunodominant antigen present in the cell wall of the fungal pathogen Coccidioides immitis, was investigated in a murine model of coccidioidomycosis. Expression plasmids for Ag2/PRA(1-18) DNA (signal sequence), Ag2/PRA(19-194) DNA (lacking the signal sequence), and Ag2/PRA(1-194) DNA (full length) were inserted in the pVR1012 vector, and the constructs were used to vaccinate the highly susceptible BALB/c mouse strain. Immunization with the signal gene sequence significantly reduced the fungal burden in the lungs and spleens of mice 12 days after intraperitoneal challenge with a lethal dose of 2,500 C. immitis arthroconidia, to a level comparable to the protection induced in mice immunized with the full-length Ag2/PRA(1-194) DNA. The Ag2/PRA(19-194) gene protected mice but to a significantly lower level than the signal sequence or the full-length Ag2 gene. The immunizing capacity of Ag2/PRA(1-18) was not attributable to a nonspecific immunostimulatory effect of DNA, as evidenced by the fact that mice immunized with a frameshift mutation of Ag2/PRA(1-18) were not protected against challenge. Furthermore, a synthetic peptide corresponding to the translated sequence of Ag2/PRA(1-18) DNA protected mice, albeit at a lower level than the Ag2/PRA(1-18) DNA vaccine. The protection induced with the signal gene vaccine correlated with the production of gamma interferon when splenocytes from Ag2/PRA(1-18)-immunized mice were stimulated with recombinant full-length Ag2 and was not associated with the production of anti-Coccidioides immunoglobulin G antibody. This is the first study to establish that a signal peptide sequence alone, administered as a gene vaccine or synthetic peptide, can induce protective immunity against a microbial pathogen.
authors.affiliation: Department of Microbiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, USA.
authors.forename: Chengyong
authors.initials: C
authors.lastname: Jiang
authors.forename: D Mitchell
authors.initials: DM
authors.lastname: Magee
authors.forename: F Douglas
authors.initials: FD
authors.lastname: Ivey
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Cox
mesh_terms: D000818:Animals; D000908:Antibodies, Fungal / Q000097:blood / Q000276:immunology; D000946:Antigens, Fungal / Q000235:genetics* / Q000276:immunology; D003045:Coccidioides / Q000235:genetics / Q000276:immunology; D003047:Coccidioidomycosis / Q000276:immunology / Q000517:prevention & control*; D004195:Disease Models, Animal; D005260:Female; D005656:Fungal Proteins; D005657:Fungal Vaccines / Q000235:genetics / Q000276:immunology*; D015870:Gene Expression; D006023:Glycoproteins / Q000235:genetics* / Q000276:immunology; D016056:Immunodominant Epitopes / Q000235:genetics* / Q000276:immunology; D007371:Interferon-gamma / Q000096:biosynthesis; D051379:Mice; D008807:Mice, Inbred BALB C; D010957:Plasmids; D021382:Protein Sorting Signals / Q000502:physiology*; D019444:Vaccines, DNA / Q000276:immunology*
chemical_list: D000908:Antibodies, Fungal; D000946:Antigens, Fungal; D005656:Fungal Proteins; D005657:Fungal Vaccines; D006023:Glycoproteins; D016056:Immunodominant Epitopes; D021382:Protein Sorting Signals; D019444:Vaccines, DNA; C102758:antigen 2, Coccidioides; D007371:Interferon-gamma