Formalin-fixed macrophages bind tumor targets similarly to viable macrophages.

Macrophages (MPs) fixed with 1% formalin in PBS bound targets similarly to viable MPs. Like binding between viable MPs and tumor cells, the process was temperature and calcium dependent. Fixed MPs discriminated targets similarly to viable MPs. Targets not bound by viable MPs were not bound by fixed MPs. The lectin Bandeiraea simplicifolia (ASI-B4) was able to enhance MP binding to tumor cells regardless of whether MPs were fixed or viable. However, it did not appear that ASI-B4-like molecules were involved in the direct recognition of F5b tumor cells by MPs. Target cells could not be fixed in 1% formalin for binding to occur. These data suggest that the receptor on the MP for tumor cell binding is functional in the absence of active physiological processes. In contrast, tumor cell processes that are dependent upon target cell viability are required for binding.