Monoclonal antibodies were prepared that recognize different age-related epitopes
on proteoglycan subunits of high buoyant density isolated from human epiphysial and
articular cartilages. Antibody EFG-4 (IgG1) recognizes a proteinase-sensitive segment
associated with the core protein. Antibody BCD-4 (IgG1) reacts with keratan sulphate
bound to core protein. Both epitopes are minimally expressed in foetal cartilage and
increase with age after birth to become maximally expressed in adult cartilage by
about 30 years of age. In contrast, monoclonal antibody alpha HFPG-846 (IgM) recognizes
a core-protein-related epitope that is maximally expressed in young foetal cartilage,
declines up to birth and thereafter and is almost absent after about 30 years of age.
Antibody alpha HFPG-846 was used to isolate by immuno-affinity chromatography two
subpopulations of proteoglycan subunits from a 16-year-old-human cartilage proteoglycan
subunit preparation. Only the antibody-unbound population showed a significant reaction
with antibodies EGF-4 and BCD-4. The amino acid and carbohydrate compositions of these
proteoglycan fractions were different, and one (antibody-bound) resembled those of
foetal and the other (antibody-unbound) resembled those of adult proteoglycans isolated
from 24-27-week-old-foetal and 52-56-year-old-adult cartilage respectively. These
observations demonstrate that human cartilages contain at least two chemically and
immunochemically distinct populations of proteoglycans, the proportions and content
of which are age-dependent. It is likely that these populations represent the products
of different genes, though their heterogeneity may be compounded by the result of
different post-translation modifications.
