C57BL/6 mouse splenocytes were stained with CD4 (clone GK1.5) FITC (filled histogram) or rat IgG2b, κ FITC isotype control (open histogram). Description CD4 is a 55 kD protein also known as L3T4 or T4. It is a member of the Ig superfamily, primarily expressed on most thymocytes, a subset of T cells, and weakly on macrophages and dendritic cells. It acts as a coreceptor with the TCR during T cell activation and thymic differentiation by binding MHC class II and associating with the protein tyrosin kinase, lck. The antibody was purified by affinity chromatography, and conjugated with FITC under optimal conditions. The CD4 antibody solution should be stored undiluted between 2°C and 8°C, and protected from prolonged exposure to light. Do not freeze. Each lot of this antibody is quality control tested by immunofluorescent staining with flow cytometric analysis. For flow cytometric staining, the suggested use of this reagent is ≤0.25 µg per million cells in 100 µl volume. It is recommended that the reagent be titrated for optimal performance for each application. Additional reported applications (for the relevant formats) include: blocking of CD4+ T cell activation1,4,11, thymocyte costimulation3, in vitro and in vivo depletion2,5-8, blocking of egg-sperm cell adhesion1,4, immunohistochemical staining of acetone-fixed frozen sections9,10, and immunoprecipitation1,2. The GK1.5 antibody is able to block CD4 mediated cell adhesion and T cell activation.Binding of GK1.5 antibody to CD4 T cells can be blocked by RM4-5 antibody, but not RM4-4 antibody. For in vivo studies or highly sensitive assays, we recommend Ultra-LEAF purified antibody (Cat. No. 100442) with a lower endotoxin limit than standard LEAF purified antibodies (Endotoxin 0.01 EU/ g). Dialynas DP, et al. 1983. J. Immunol. 131:2445. (Block, IP) Dialynas DP, et al. 1983. Immunol. Rev. 74:29. (IP, Deplete) Wu L, et al. 1991. J. Exp. Med. 174:1617. (Costim) Godfrey DI, et al. 1994. J. 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Cell Stem Cell. 28(7):1248-1261.e8. PubMedVolberding PJ, et al. 2021. Cell Reports. 35(8):109160. PubMed 1. Barclay A, et al. 1997. The Leukocyte Antigen FactsBook Academic Press. 2. Bierer BE, et al. 1989. Annu. Rev. Immunol. 7:579. 3. Janeway CA. 1992. Annu. Rev. Immunol. 10:645. TCR-CD3 complexes on the T-lymphocyte surface are rapidly downregulated upon activation with peptide-MHC complex, superantigen or cross-linking with anti-TCR or anti-CD3 antibodies. PMA/Ionomycin treatment has been shown to downregulate surface CD4 expression. Receptor downregulation is a common biological phenomenon and so make sure that your stimulation treatment is not causing it in your sample type. For research use only. Not for diagnostic use. Not for resale. 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