The most impoant function of epithelioid cells in tuberculosis is -

Epithelioid cells. These are so called because of their epithelial cell-like appearance, are modified macrophages/ histiocytes which are somewhat elongated, having a vesicular and lightly-staining slipper-shaped nucleus, and pale staining abundant cytoplasm with hazy outlines so that the cell membrane of adjacent epithelioid cells is closely apposed.Epithelioid cells are weakly phagocytic. It is suggested that epithelioid cells could play an impoant role in fibrosis possibly by the secretion of a fibroblast activating factor. Ref:Harsh Mohan - Textbook of Pathology, 6th Edition.page no.148 &Immunobiology,elsevier,Volume 221, Issue 12, Pages 1329-1432.