Bystander T cells in human immune responses to dengue antigens.
BACKGROUND
Previous studies of T cell activation in dengue infection have focused on restriction of specific T cell receptors (TCRs) and classical MHC molecules. However, bystander T cell activation, which is TCR independent, occurs via cytokines in other viral infections, both in vitro and in vivo, and enables T cells to bypass certain control checkpoints. Moreover, clinical and pathological evidence has pointed to cytokines as the mediators of dengue disease severity. Therefore, we investigated bystander T cell induction by dengue viral antigen.


RESULTS
Whole blood samples from 55 Thai schoolchildren aged 13-14 years were assayed for in vitro interferon-gamma (IFN-γ) induction in response to inactivated dengue serotype 2 antigen (Den2). The contribution of TCR-dependent and independent pathways was tested by treatment with cyclosporin A (CsA), which inhibits TCR-dependent activation of T cells. ELISA results revealed that approximately 72% of IFN-γ production occurred via the TCR-dependent pathway. The major IFN-γ sources were natural killer (NK) (mean ± SE = 55.2 ± 3.3), CD4+T (24.5 ± 3.3) and CD8+T cells (17.9 ± 1.5), respectively, as demonstrated by four-color flow cytometry. Interestingly, in addition to these cells, we found CsA-resistant IFN-γ producing T cells (CD4+T = 26.9 ± 3.6% and CD8+T = 20.3 ± 2.1%) implying the existence of activated bystander T cells in response to dengue antigen in vitro. These bystander CD4+ and CD8+T cells had similar kinetics to NK cells, appeared after 12 h and were inhibited by anti-IL-12 neutralization indicating cytokine involvement.


CONCLUSIONS
This study described immune cell profiles and highlighted bystander T cell activation in response to dengue viral antigens of healthy people in an endemic area. Further studies on bystander T cell activation in dengue viral infection may reveal the immune mechanisms that protect or enhance pathogenesis of secondary dengue infection.
Suwannasaen
Duangchan
D
The Centre for Research and Development of Medical Diagnostic Laboratories, Faculty of Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
Romphruk
Arunrat
A
Leelayuwat
Chanvit
C
Lertmemongkolchai
Ganjana
G
D000293:Adolescent; D019138:Antibodies, Blocking / Q000494:pharmacology; D000956:Antigens, Viral / Q000276:immunology* / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D003716:Dengue Virus / Q000276:immunology*; D005260:Female; D006801:Humans; D007111:Immunity, Cellular; D007371:Interferon-gamma / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D018664:Interleukin-12 / Q000276:immunology; D007694:Killer Cells, Natural / Q000187:drug effects / Q000276:immunology; D008297:Male; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism; D037182:T-Cell Antigen Receptor Specificity; D013785:Thailand
D019138:Antibodies, Blocking; D000956:Antigens, Viral; D011948:Receptors, Antigen, T-Cell; D018664:Interleukin-12; D007371:Interferon-gamma; D016572:Cyclosporine