Antigen presenting cells in situ: their identification and involvement in immunopathology.

Macrophages and other dendritic non-lymphoid cells have been shown to be functionally capable of presenting antigen to induce lymphocyte responses. These cells can now be studied in situ and distinguished, one from another, within normal tissues and sites of cellular infiltration. Analysis of the microenvironment within which these cells are found can be made with immunohistological methods using monoclonal antibodies (McAbs) and cytochemical techniques. In some cases McAbs are specific for particular types of antigen presenting cell. Using such reagents, evidence is accumulating that these cells may be intimately involved in the pathogenesis of immunoregulatory disorders. What is now required is a more definitive correlation between functional capacity and cell phenotype established with cells isolated from blood, and from normal and pathological tissues. If this is possible the immunopathologist may be able, not only to analyse complex microenvironments but also directly determine the interactions and mechanisms at play within the diseased tissues.