The 2.43-CP128 monoclonal antibody is a chimeric version of the original 2.43 antibody. The variable domain sequences are identical to the original 2.43 but the constant region sequences have been switched from rat IgG2b to mouse IgG2b. The 2.43-CP128 antibody contains no Fc mutations just as the original rat IgG2b antibody does not. The 2.43-CP128 monoclonal antibody reacts with mouse CD8α. The CD8 antigen is a transmembrane glycoprotein that acts as a co-receptor for the T cell receptor (TCR). Like the TCR, CD8 binds to class I MHC molecules displayed by antigen presenting cells (APC). CD8 is primarily expressed on the surface of cytotoxic T cells, but can also be found on thymocytes, natural killer cells, and some dendritic cell subsets. CD8 most commonly exists as a heterodimer composed of one CD8α and one CD8β chain however, it can also exist as a homodimer composed of two CD8α chains. Both the CD8α and CD8β chains share significant homology to immunoglobulin variable light chains. The molecular weight of each CD8 chain is approximately 34 kDa.

See the references for the original rat IgG2b 2.43 antibody (https://bioxcell.com/invivoplus-anti-mouse-cd8a-bp0061).