Summary
Cellular sites of coagulation activation within complex, intact tissues have been
studied by immunohistochemical techniques. Hirudin, a specific and high affinity inihibitor
of the active site of thrombin, together with antibody to hirudin were applied to
sections of AMeX-fixed specimens of normal lung, kidney, placenta, freshly incised
skin and unperturbed skin obtained at fresh autopsy; to rheumatoid synovial tissue;
and to malignant tissue from a variety of tumor types. Staining for thrombin was observed
selectively on pulmonary alveolar, rheumatoid synovial, and placental macrophages
that express an intact extrinsic coagulation pathway. Staining was also observed restricted
to the endothelium of capillaries in freshly incised skin but not in either unperturbed
skin or in aged incisions. Staining of tumor cell bodies was observed in small cell
carcinoma of the lung, renal cell carcinoma, and malignant melanoma tissues that we
found previously to show tumor cell-associated procoagulant activity. This staining
occurred commonly on cells within the tumor mass that were distant from stromal fibrinogen/fibrin.
By contrast, tumor-associated macrophage but not tumor cell staining was seen in adenocarcinoma
and squamous cell carcinoma of the lung, and little or no staining was seen in colon
cancer tissue. Negative controls in which either the hirudin probe or its antibody
were omitted failed to show staining. These results are in accord with previous findings
and suggest that such techniques may be useful for studying the cellular sites of
thrombin generation in intact tissues. We postulate that administration of potent
and specific thrombin antagonists, such as hirudin, to patients with relevant tumor
types might be followed by homing of hirudin to tumor cells in vivo so that effects
of local thrombin generation on malignant progression can be determined.
