CD40 and Sepsis: Although the use of functional assays to assess APC-effector T lymphocyte interactions as well as detecting the antigen density of co-stimulatory molecules (CD80, CD86, and CD40) on the monocyte cell surface would be ideal, in clinical practice mHLA-DR analysis is well established and a standardised [25] bedside assay [48] that has been previously utilised in clinical trials of sepsis immuno-modulation [26].