Analysis of carbohydrate structures in basal laminar deposit in aging human maculae.

OBJECTIVE

To analyze carbohydrate structures in basal laminar deposit (BLD), an extracellular material that accumulates between the retinal pigment epithelium (RPE) and Bruch's membrane. BLD has been shown to correlate positively with visual loss in age-related macular degeneration.

METHODS

Thirteen postmortem human maculae with BLD were histochemically examined by light microscopy using the monoclonal antibody HNK-1 and seven lectins; canavalia ensiformis (ConA), soybean agglutinin (SBA), wheat germ agglutinin (WGA), dolichos bifloris (DBA), ulex europaeus (UEA-I), ricinius communis agglutinin I (RCA-I), and peanut agglutinin (PNA). Three maculae were stained with polyclonal antibodies against laminin and collagen type IV.

RESULTS

BLD was exclusively stained by DBA and SBA, whereas Con A, WGA, UEA-I, RCA-I, and HNK-1 stained various other structures in the human macula as well. The main part of the BLD adjacent to Bruch's membrane stained with these lectins and the monoclonal antibody HNK-1, whereas only a small part of the BLD adjoining the RPE stained with antibodies against laminin and collagen type IV. Drusen stained neither with any lectin nor with any antibody.

CONCLUSIONS

DBA and SBA, which bind specifically to an alpha-D-GalNAc moiety, are specific markers for the light-microscopic detection of BLD in human macular tissue. Furthermore, the authors conclude that BLD contains several carbohydrate structures other than the carbohydrate moieties on laminin and collagen type IV. If drusen contain carbohydrate structures, these must be different from those in BLD.