Cartilage contains mixed fibrils of collagen types II, IX, and XI.

TLDR

Immunoelectron microscopy of 17‑day chick embryo sternal cartilage fibril fragments was used to map collagen XI distribution with specific polyclonal antibodies. The study found that collagen XI, along with collagens II and IX, is uniformly incorporated into cartilage fibrils, but collagen XI is antigenically masked in intact fibrils and only detectable where the structure is partially disrupted, confirming its integral, homogeneous presence in the cartilage network.

Abstract

The distribution of collagen XI in fibril fragments from 17-d chick embryo sternal cartilage was determined by immunoelectron microscopy using specific polyclonal antibodies. The protein was distributed throughout the fibril fragments but was antigenically masked due to the tight packing of collagen molecules and could be identified only at sites where the fibril structure was partially disrupted. Collagens II and IX were also distributed uniformly along fibrils but, in contrast to collagen XI, were accessible to the antibodies in intact fibrils. Therefore, cartilage fibrils are heterotypically assembled from collagens II, IX, and XI. This implies that collagen XI is an integral component of the cartilage fibrillar network and homogeneously distributed throughout the tissue. This was confirmed by immunofluorescence.