Expression of HLA‐A, B, C, β2‐microglobulin (β2m), HLA‐DR, ‐DP, ‐DQ and of HLA‐D‐associated invariant chain (Ii) in soft‐tissue tumors

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Abstract
Non‐neoplastic mesenchymal cells, along with 33 benign and 87 malignant soft‐tissue tumors (STT) were examined for expression of HLA‐A, B, C, β2‐microglobulin (β2m), HLA‐DR, ‐DP, and ‐DQ molecules and the HLA‐D associated invariant chain (Ii). Serial frozen sections were immunostained using monoclonal antibodies (MAbs) to monomorphic framework determinants of HLA sublocus products, β2m and li, and to CD53, a recently defined broadly distributed pan‐leucocyte molecule. Compared with the normal state, an induction/neo‐expression of HLA‐A, B, C/β2m was found in a considerable number of tumors of muscle, peripheral nerve, cartilageforming, adipose, and vascular tissues. Conversely, some tumors of fibrous origin and of autonomic ganglia showed an abnormal abrogation/loss of HLA‐A, B, C/β2m with respect to their cells of origin. Small, round tumor cells present in various types of STT exhibited a heterogenous pattern of expression of these molecules with a preponderance of HLA‐A, B, C/β2m‐negativity. HLA‐D/Ii determinants were rarely detectable in STT. Besides their expression in some fibrohistiocytic tumors, they were only occasionally found in tumors of smooth‐muscle, peripheral‐nerve and vascular origin as well as in one clear‐cell sarcoma. In all tumors but one, there was no microtopographic association between HLA‐D/Ii‐positive tumor cells and inflammatory cells. CD53 allowed discrimination between dendritic interstitial cells (DIC) and neoplastic cells and additionally revealed that, in contrast to other solid tumors, STT are generally characterized by an extreme scarcity of lymphohistiocytic infiltrates. Our data indicate that, aside from very rare exceptions, aberrant induction or abrogation of MHC molecules in STT occurs in the absence of lymphohistiocytic stromal infiltrates, suggesting that these alterations might not be a consequence of local cytokine effects.