Fluorescent granular cells of the thymus can be identified as dendritic macrophages.

Fluorescent granular cells of the thymus lobule containing neurotransmitter monoamines express Ia antigen and S-100 protein, which attests to their macrophage origin; positive staining with aldehyde fuchsin points to secretion of peptide hormones by these cells. These facts and the absence of phagocytic activity allow to identify these cells as dendritic macrophages.