Type II collagen during cartilage and corneal development: Immunohistochemical analysis with an anti‐telopeptide antibody

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Abstract
We have examined the pattern of immunoreactivity of a monoclonal antibody, II‐5B2, with specificity for an epitope which resides within the NH2‐terminal extension peptide (telopeptide) of the avian type II collagen molecule. This epitope is available in regions of matrix where de novo synthesis of the molecule is ongoing, but not where synthesis has ceased and maturation and crosslink formation have occurred. Within the cartilaginous growth plate, the epitope disappears from the matrix soon after the chondrocytes become hypertrophic; within the cornea, the epitope disappears subjacent to the epithelium. The II‐5B2 epitope is not made available by a variety of procedures shown to remove potentially masking substances and to disrupt fibrillar organization. It is rendered available, however, when covalent crosslink formation between collagen molecules is blocked through administration of β‐aminopropionitrile or penicillamine. In contrast, the epitope of another monoclonal antibody against type II collagen, II‐II6B3, which resides in the triple‐helical domain of the molecule, in cartilage is present throughout the growth plate including the hypertrophic zone, and in cornea extends for a considerable distance into the stroma. Thus, it is available for antibody binding regardless of fibril maturation and crosslinking. These data suggest that the II‐5B2 epitope becomes unavailable when the telopeptide becomes cross‐linked. By using these two monoclonal antibodies in serial sections, one can establish the crosslinking pattern of type II collagen in the tissue. This set of antibodies is a potentially useful tool for analyzing normal and abnormal development, remodeling, and repair processes in the skeletal system and in other tissues where type II collagen is involved in organization of the matrix, such as the primary corneal stroma.