Is the presence of serologically defined target cell antigens sufficient for binding of cytotoxic T lymphocytes?

Target cell parameters that coincide with specific binding (conjugation) of target cells to cytotoxic T lymphocytes were examined. It was demonstrated that concentrations of formaldehyde (0 to 1.2%) which do not affect the capacity of target cells to exclude dyes and incorporate sodium chromate, or their susceptibility to cellular and humoral immune lysis did not affect target cell conjugation. Treatments with higher formaldehyde concentrations (1.6 to 3.2%) caused similar decreases in all of the above-mentioned target cell parameters. Formaldehyde-treated (over 0.1%) targets that could not cap alloantigens or incorporate macromolecular precursors could still conjugate with cytotoxic T lymphocytes. Quantitative changes of serologically detected antigens alone cannot account for the decrease in binding of formaldehyde (greater than 1.2%)-treated target cells to cytotoxic T lymphocytes, since absorption of lytic alloantibodies by formaldehyde-fixed targets was not affected over the fixative range used (0 to 3.2%). From this study, it appears that certain target cell properties related to membrane structure and function and not the apparent expression of serologically defined antigens alone are essential for binding of targets by cytotoxic T lymphocytes. Additionally, it was shown that target cell susceptibility to immune lysis is retained, as long as their ability to bind to cytotoxic T lymphocytes is not affected.