Multiplex assay for quantification of acute phase proteins and immunoglobulin A in dried blood spots.

Inflammation is the first line defense mechanism against infection, tissue damage or cancer development. However, inappropriate inflammatory response may also trigger diseases. The quantification of inflammatory proteins is essential to distinguish between harmful and beneficial immune response. Currently used immunoanalytical assays may suffer specificity issues due to antigen-antibody interaction and possible cross-reactivity of antibody with other protein species. In addition, immunoanalytical assays typically require invasive blood sampling and additional logistics; they are relatively costly and highly challenging to multiplex. We present a multiplex assay based on selected reaction monitoring (SRM) for quantification of seven acute phase proteins (i.e. SAA1, SAA2-isoform1, SAA4, CRP, A1AT isoform1, A1AG1, A1AG2) and the adaptive immunity effector IGHA1 in dried blood spots (DBS). This type of samples is readily available from all human subjects including newborns. The study utilizes proteotypic isotopically labeled peptides with trypsin-cleavable tag and presents optimized and reproducible workflow and several important practical remarks regarding quantitative SRM assays development. The panel of inflammatory proteins was quantified with sequence specificity capable to differentiate protein isoforms with intra- and inter-day precision (<16.4% CV; <14.3% CV respectively). Quantitative results were correlated with immunonephelometric assay (typically >0.9 Pearson's R).