Abundance of interstitial heparan sulfate in granuloma annulare but not in other mucinous skin diseases

Mucin as a diagnostic clue in dermatopathology

Mucins are high-molecular weight glycoproteins typically found in normal skin in small amounts. There are several reports regarding different types of cutaneous mucinosis. In this report, we discuss mucins in dermatopathology as a diagnostic clue of some well-known entities and some less frequent cutaneous diseases. We also emphasize mucin as a sign in the differential diagnosis between conditions that show histopathological overlap. Lastly, we discuss the locations and circumstances in which mucin could be considered almost normal or physiological.

Interstitial heparan sulfate in granulomatous inflammatory skin diseases

BACKGROUND

Heparan sulfate (HS) is a glycosaminoglycan that is anchored to the outside of cell membranes. Under ordinary circumstances, it is not present in the interstitium, but under certain circumstances, mainly in the setting of inflammation and tissue repair, HS can be shed from the cell surface into the interstitium in a regulated fashion. Under these circumstances, interstitial HS seems to have an immunomodulatory function because of its binding of many cytokines. However, it is not known which cell types present at an inflammatory site are responsible for this shedding.

OBJECTIVE

We have investigated the presence of interstitial HS by immunohistochemistry in various inflammatory skin diseases characterized by different compositions of the inflammatory infiltrate.

RESULTS

Strong interstitial HS immunoreactivity was present only in diseases with a predominantly histiocytic infiltrate but not in diseases with a predominantly lymphocytic or neutrophilic infiltrate.

CONCLUSIONS

This indicates that histiocytes have a direct or indirect role in the HS shedding process. In the well-formed granulomas of sarcoidosis, interstitial HS immunoreactivity was spatially associated with the fibrotic ring at the periphery of the granulomas, but not with the center harboring the histiocytes. This suggests that histiocytes can stimulate fibroblasts to shed HS into the interstitium.