Description: The OX35 monoclonal antibody reacts with rat CD4. CD4 is a co-receptor which participates in signaling through the T cell receptor by making contacts with MHC class II expressed on antigen-presenting cells (APC). CD4 is expressed in the thymus by CD4+CD8+ "double-positive" and CD4+ "single-positive" thymocytes, and by CD4+ "helper" T cells in the periphery. CD4 is a cell-surface membrane glycoprotein which contains four extracellular immunoglobulin-like domains.