FIGURE 4.

TSG-6/HC2-generated HMW IαI proteins are HC donors. Shown is a Coomassie Blue-stained reduced SDS-PAGE gel showing samples of IαI (lane 1), IαI incubated with TSG-6 (lane 2), IαI incubated with TSG-6 and HA oligosaccharides simultaneously (lane 3), and IαI incubated with TSG-6, where HA oligosaccharides were subsequently added (lane 4). The incubation of IαI and TSG-6 generates HMW IαI, and because only trace amounts of these species are present after a subsequently incubation with HA oligosaccharides, it seems likely that the HMW IαI species serve as HC donors. To confirm the identity of the generated HC·HA complexes, the proteins of interest were excised (bands a–c) and subjected to peptide mass fingerprinting (supplemental Table S1). These analyses demonstrate that band a contains HC1 and HC2, band b contains HC2, and band c contains HC1.