We detected a significant decrease in IgG2a and IgG2b but not in IgG1 in the STAT4?/? mice. the levels of IgG2a, IgG2b, and IgG3 in the sera of STAT4?/? mice when compared to the control BALB/c mice. Conclusions These results suggest that the absence of TH1 cytokine reactions did alter safety against viral replication and IgG isotypes but not vision disease or survival. Introduction Transmission transducers and activators of transcription (STAT) proteins are triggered in response to a large number of cytokines, growth factors, and hormones . Upon activation following a binding of ligands to their receptors, STAT proteins dimerize, translocate to the nucleus, and bind to the promoters of specific target genes. At present the STAT family is classified into seven organizations  of cytoplasmic proteins, which are triggered by phosphorylation of a specific tyrosine . Although some cytokines and growth factors can activate multiple STAT proteins, certain STAT proteins are triggered with substantial specificity. In turn, each triggered STAT protein activates transcription of a specific cytokine. For example, STAT6 is involved in production of several interleukins (IL) such as IL-4 and IL-13 [4,5], while STAT4 is definitely involved in Ac-DEVD-CHO production of IL-2 [6,7]. Therefore, STAT6?/? mice have a reduced T-helper 2 (TH2)-mediated immune response, while STAT4?/? mice have an increased TH2-mediated immune response. Following activation by foreign antigens, CD4+ and CD8+ T-cell clones of mice and humans produce specific patterns of cytokine expression [8,9]. Ac-DEVD-CHO Based on the cytokines produced, CD4+ T cells are designated TH1 or TH2, and CD8+ T cells are designated TC1 or TC2 [8,10,11]. Usually, either a TH1/TC1 or a TH2/TC2 cytokine pattern predominates in response to a specific antigenic challenge [12-14]. TH1/TC1 cells are involved in cellular immunity (delayed type hypersensitivity and cellular cytotoxicity) and produce IL-2, tumor necrosis factor beta (TNF-), and interferon-gamma (IFN-). TH2/TC2 cells are involved in humoral immunity (antibody mediated) and produce IL-4, IL-5, IL-6, and IL-10 [9,15]. IL-4 enhances TH2/TC2 development and inhibits TH1/TC1 development [16,17]. IL-2 stimulates development of TH1/TC1 and inhibits development of TH2/TC2 [18,19]. The TH1/TC1 to TH2/TC2 balance determines the outcome of a wide variety of immune responses involving infectious, autoimmune, and allergic diseases . We previously exhibited faster clearance and lower vision disease in STAT6?/? mice . These results indicated that increased level of IL-2 in STAT6?/? mice was associated with improved vaccine efficacy. Immunohistochemical analyses of corneal sections of ocularly infected mice had shown that lack of protection against corneal scarring (CS) correlated with the absence of neutralizing antibody titer and the presence of IL-4 in the cornea [13,21]. Since IL-4 is an indicator of a TH2 response [8,14], these results suggested that TH2 responses are either neutral or enhance CS [13,22]. The studies presented here with STAT4?/? mice, which are deficient in IL-2 production and lack a TH1 response, were undertaken to determine if these observed correlations reflected function. We report that this absence of TH1 and elevation of TH2 responses in STAT4?/? mice had no role Ac-DEVD-CHO in protection against ocular herpes simpex computer virus type 1 (HSV-1) contamination but Itgb1 did have an effect on immunoglobulin-G (IgG)-subtype switching and early viral replication. Methods Computer virus and cells Plaque-purified HSV-1 strains (maintained in-house) were produced in Ac-DEVD-CHO rabbit skin (RS) cell monolayers in minimal essential media (MEM) made up of 5% fetal bovine serum. McKrae, a stromal disease-causing neurovirulent HSV-1 strain was the ocular challenge computer virus. Ac-DEVD-CHO KOS, a avirulent nonstromal disease-producing strain was used as a live computer virus vaccine. Mice All animal procedures adhered to the Association for Research in Vision and Ophthalmology (ARVO) statement for the Use of Animals in Ophthalmic and Vision Research and according to institutional animal care and use guidelines. Six-week-old inbred BALB/c mice and homozygous BALB/c-STAT4?/? mice (Jackson Laboratory, Bar Harbor, ME) were used in this study. Vaccinations of mice Mice were vaccinated three times intraperitoneum (IP) at 3-week intervals with 2105 plaque-forming models (PFU) of live KOS in tissue culture media. Mock-vaccinated mice were similarly inoculated but with tissue culture media (MEM with %5 FBS) alone. Serum-neutralizing antibody titers were determined by 50% plaque reduction assays, as we described previously , using sera collected 3 weeks after the final vaccination. Briefly, the sera from vaccinated or mock-vaccinated mice were heat inactivated for 30 min. at 56 C, diluted in MEM, mixed with 200 PFU of HSV-1 strain McKrae, and incubated for 30 min at 37 C. Samples were added to RS cells in 6-well microtiter plates, the.