Differential survival of albumin in ancient bone

The identification of blood proteins in ancient bone is important (1) because detection of simple proteins can give information on species specificity and evolution, and (2) because the methods used provide a sound technical basis for investigating the survival of more informative proteins, such as HLA and blood groups, which would shed light on genetic profiles and disease predispositions of ancient populations. Our previous studies used a sensitive and specific enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies and showed that albumin can be identified in human skeletal remains at least 4000 years old. However, the factors which affect survival and diagenesis of proteins within ancient bone remain largely unresolved. In the present studies, the results obtained after testing extracts of ancient bovine and human bone for albumin with the ELISA have been compared. The human extracts were prepared from intact ("closed") vertebrae from formal burial sites. Well-preserved bovine material, on the other hand, could not easily be found and most of the bovine extracts had to be prepared from assemblages of bone which were "open" (i.e. the spongy interior was exposed), either because of butchering or weathering. Although albumin could be detected in both bovine and human bones which were several thousand years old, the survival pattern between the species was strikingly different (chi-square=11·7,P<0·001); albumin was identified in 23 of the 31 human extracts but in only two of the 14 bovine ones. The assay for bovine albumin was as sensitive as that for human albumin and had been equally successful in identifying blood stains on buried samples of gauze. As part of the present studies, a modern experiment was also performed in which "open" fragments of bovine and human bone were buried in a suburban garden exposed to high rainfall and exhumed and tested at set intervals over a 26-month period. The results showed a pattern of albumin survival similar to that observed with the ancient bovine bone, i.e. survival was much poorer than with the intact "closed" bone from the ancient human burials. It was concluded that bone integrity is of great importance for protein survival and that exposure of marrow and trabecular bone to the physical and chemical effects of water is the most significant single factor in the production of diagenetic changes. In this respect, water appears to have a far greater effect than age, soil content, pH or heat.