Recognizes a protein of 55 kDa, identified as CD4. CD4 is a membrane glycoprotein of T lymphocytes that interacts with major histocompatibility complex class II antigens and is also a receptor for the human immunodeficiency virus. This protein is expressed not only in T lymphocytes, but also in B cells, macrophages, and granulocytes. It is also expressed in specific regions of the brain. The protein functions to initiate or augment the early phase of T-cell activation, and may function as an important mediator of indirect neuronal damage in infectious and immune-mediated diseases of the central nervous system. Multiple alternatively spliced transcript variants encoding different isoforms have been identified.Primary antibodies are available purified, or with a selection of fluorescent CF Dyes and other labels. CF Dyes offer exceptional brightness and photostability. Note: Conjugates of blue fluorescent dyes like CF405S and CF405M are not recommended for detecting low