The immunohistochemical localisation of microfibril-associated glycoprotein (MAGP) in elastic and non-elastic tissues.

We have previously identified the major antigen of elastin-associated microfibrils as a 31kD glycoprotein which we named microfibril-associated glycoprotein or MAGP. Affinity-purified antibodies to MAGP were shown to localise specifically to elastin-associated microfibrils in sections of bovine foetal nuchal ligament. In the present paper we compare the localisation of anti-MAGP antibodies and anti-tropoelastin antibodies in a range of bovine elastic and non-elastic tissues. The results show that anti-MAGP antibodies invariably localised to immuno-reactive elastic fibres, wherever they occurred. Extensive additional localisation was observed in a number of tissues. This extra distribution of anti-MAGP antibodies was found to correspond to those structures exhibiting the oxytalan histochemical staining reaction in tissues such as skin, periodontal ligament and ocular zonule. Since these oxytalan fibres have been shown to consist of 12 nm microfibrils which are morphologically similar to those of elastic fibres (and unpublished data from this laboratory confirm this conclusion), the results suggest that MAGP is a component of 12 nm microfibrils in both elastic and non-elastic tissues. Anti-tropoelastin antibodies did not localise to these oxytalan fibres, suggesting that tropoelastin is not a component of 12 nm microfibrils. MAGP was also detected in extracellular matrix regions of tissues such as skeletal muscle, Achilles tendon and spleen, suggesting that 12 nm microfibrils, containing one or more macromolecular constituents in common, make up an important structural system within the extracellular matrix in a wide range of elastic and non-elastic tissues.