Innate and acquired immunity to herpes simplex virus type 2 glycoprotein G in humans

Abstract

Herpes simplex virus type 2 (HSV-2) is a sexually transmitted pathogen that infects the human genital tract mucosa and is the most common cause of genital ulcer disease in humans. The infection exhibits a broad clinical spectrum, ranging from severe recurrent episodes of genital herpes to being completely asymptomatic. The overall objective of the present thesis was to characterize the cellular immune responses to HSV-2 glycoprotein G (gG-2) in symptomatic patients, symptom-free carriers, and uninfected controls.The first aim of this thesis was to characterize the T-cell response to the membrane-bound (mgG-2) and the secreted portion of HSV-2 glycoprotein G (sgG-2) in symptomatic and asymptomatic individuals. Patients with symptomatic HSV-2 infection were recruited from regional STD clinics. Asymptomatic HSV-2 carriers were recruited among partners to these patients. HSV-2 gG-2- and gG-2-derived peptide-specific T-cell proliferative responses and cytokine production were measured. We show that both sgG-2 and mgG-2 are HSV-2 type-specific T-cell antigens that induce both proliferative and cytokine responses in HSV-2-infected individuals. The T-cell proliferative responses fluctuated with time, and did not differ between asymptomatic and symptomatic individuals. In contrast, patients with recurrent genital herpes had a reduced HSV-2-specific Th1 response compared to asymptomatic carriers, implying that a functional Th1 response is a prerequisite for adequate anti-viral immune control. We also identified an immunodominant region within the secreted portion of gG-2, although no universal T-cell epitope was apparent. The second aim of this thesis was to investigate whether sgG-2 could activate cells of the innate immune system. Monocytes, neutrophils and NK cells were isolated from healthy blood donors. The production of oxygen radicals was measured by luminol-enhanced chemiluminescence and chemotaxis was assayed in the trans-well migration system. The effects of oxygen radicals on NK cell cytotoxicity and viability were determined by FACS analysis and conventional cytotoxicity assays. We discovered that two gG-2-derived peptides induced the production of oxygen radicals by phagocytes. One of the peptides, gG-2p20, acted as a ligand for the formyl peptide receptor and induced the chemotaxis of both neutrophils and monocytes. The second peptide, gG-2p19 is probably a ligand for the formyl peptide receptor-like 2. The gG-2p19 peptide activated the monocyte NADPH oxidase, but it was not chemotactic. Finally, we have shown that NK cell function and viability are hampered in the presence of gG-2p20-activated phagocytes through their release of oxygen radicals.In conclusion, our results show that patients with recurrent genital herpes have impaired Th1 responses compared to asymptomatic HSV-2 carriers. Further, we have also determined that two HSV-2 sgG-2 peptides affects phagocyte and NK cell functions.