Lymphohistiocytic

Lymphohistiocytic is a descriptive term used in pathology to indicate that a tissue infiltrate contains both lymphocytes and histiocytes (macrophages). It denotes the cellular composition of the inflammatory response rather than a specific disease. Lymphocytes are small cells with scant cytoplasm, while histiocytes are larger macrophage-lineage cells; in some contexts histiocytes may be activated and form epithelioid or foamy forms, and multinucleated giant cells can be seen in granulomatous settings.

This pattern may be observed in a wide range of conditions, including chronic inflammatory diseases, infectious processes (especially those with granuloma formation), autoimmune disorders, and tissue changes after injury or therapy. The arrangement of the cells—whether diffuse, perivascular, nodular, or focal—along with accompanying histologic features, can help guide differential diagnosis but is not diagnostic on its own. Immunohistochemical staining can aid in characterization, with lymphocytes typically expressing markers such as CD3 for T cells and CD20 or CD79a for B cells, and histiocytes expressing markers like CD68 or CD163.

Because lymphohistiocytic infiltration is a descriptive pattern rather than a defined disease, its clinical significance depends on the broader clinical context, laboratory findings, and additional histopathologic features. Pathology reports may describe a lymphohistiocytic infiltrate to convey the mixed cellular nature of the inflammatory response and to prompt consideration of potential etiologies in conjunction with patient history.