Mouse CD4 (L3T4) MicroBeads are suitable for positive selection or depletion of mouse T helper cells from single-cell suspensions of lymphoid and non-lymphoid tissues or from peripheral blood. The CD4 antigen is expressed on most thymocytes and mature T helper cells, and at lower levels on a subpopulation of dendritic cells. CD4 acts as an accessory molecule in the recognition of MHC class II/peptide complexes by the TCR heterodimer on CD4+ T helper cells. The CD4 antigen is expressed on approximately 90% of thymocytes, 25% of splenocytes, and 55% of lymph node cells.