Application of monoclonal antibodies to the characterization of cells eluted from human articular cartilage. Expression of Ia Antigens in Certain Diseases and Identification of an 85‐kD Cell Surface Molecule Accumulated in the Pericellular Matrix

Ia antigens were strongly expressed on a considerable proportion of cells eluted from the damaged articular cartilages of certain individuals with osteoarthritis, rheumatoid arthritis, traumatic arthritis, or from osteochondromas. In contrast, la antigens were found on less than 1% of cells eluted from the more normal appearing cartilage of certain other patients with osteoarthritis, rheumatoid arthritis, osteonecrosis, femoral neck fractures, an enchondroma, and a chondrosarcoma. The cell preparations obtained from these latter individuals consisted of clusters of 1–4 chondrocytes embedded in a surrounding island of the pericellular matrix, whereas as in the samples that yielded lapositive cells, many chondrocytes were isolated as free cells without a surrounding matrix. The la antigens were detected primarily on this latter cell population, suggesting that their expression might indicate a chondrocyte activated to alter its surrounding matrix. The cytologic features of the la‐positive cells were indistin guishable from those of the la‐negative chondrocytes. All eluted cells lacked antigens of the monocyte, B cell, or T cell lineages. An antigen detected by the monoclonal reagent MϕR‐17 was identified on the membrane of large numbers of chondrocytes, both with and without the pericellular matrix, indicating that the matrix in these preparations was permeable to molecules the size of antibodies. A monoclonal antibody 83c2, demonstrated to react with an 85‐kD surface molecule expressed on certain fibroblastoid and other cells, detected an antigen present on the majority of normal chondrocytes and in varying percentages of cartilage cells obtained from patients with osteoarthritis or rheumatoid arthritis. Of special interest, the periphery of the pericellular matrix was stained by this reagent in an irregularly distributed ring‐like zone, suggesting that the 83c2 molecule was shed into the matrix from the cell surface and accumulated in these areas.