IgA-type macroprolactin among 130 patients with macroprolactinemia.

Objectives: Macroprolactin (macro-PRL) mostly comprises a complex of PRL with IgG. The aim of this study was to clarify whether IgA-type macro-PRL exists and, if so, to elucidate the prevalence of and differences in laboratory data from IgG-type.

Methods: One hundred thirty patients with macroprolactinemia who were diagnosed through screening via the polyethylene glycol precipitation method followed by confirmation using gel filtration chromatography (GFC) were examined. IgA-type and IgG-type macro-PRLs were identified via Jacalin column/SDS‒PAGE and protein G columns, respectively.

Results: SDS‒PAGE under nonreducing conditions followed by western blotting with an IgA antibody revealed that the fraction bound to the Jacalin column was actually IgA. The PRL band was detected at the same position as the IgA band, which was purified with a Jacalin column, suggesting that PRL was bound to IgA. The finding that the PRL band was observed not only at the same position as IgA but also at the same position as the 23 kDa PRL reference suggested that some PRL dissociated from IgA during SDS‒PAGE. The prevalence rates of macro-PRL of only IgA, IgA plus IgG, only IgG, and non-IgA/non-IgG types were 7.7, 3.1, 83.8, and 5.4 %, respectively. Neither the PEG precipitation ratios of PRL nor the macro-PRL ratios on GFC differed between IgA- and IgG-type macro-PRLs, whereas both ratios were significantly lower in non-IgA/non-IgG-type macro-PRL.

Conclusions: IgA-type macro-PRL was demonstrated to exist. IgG-type macro-PRL was most prevalent, followed by IgA, non-IgA/non-IgG and IgA plus IgG-type macro-PRLs.