Chemically-blocked antibody microarray for multiplexed high-throughput profiling of specific protein glycosylation in complex samples

Analysis of serum alpha-fetoprotein (AFP) and AFP-L3 levels by protein microarray

Objectives

This study aimed to examine a simple, effective, time-saving, and low-cost protein microarray method for detecting serum alpha-fetoprotein (AFP) and AFP-L3 levels.

Methods

Serum samples from patients with hepatocellular carcinoma (HCC) (n = 33) and control subjects (n = 39) were collected and evaluated for the presence of AFP using a novel protein microarray. Glycoprotein (including AFP-L3) was enriched from crude samples by a Hotgen Biotech glycosyl capture spin column and then detected by protein microarray. An electrochemiluminescence immunoassay (ECLIA) was used to validate the measured values.

Results

Neither AFP levels lower than 20 ng/mL in the HCC group nor AFP levels higher than 20 ng/mL in the control group were found when tested by the ECLIA and protein microarray. The kappa test showed good consistency in the diagnostic performance of measuring serum AFP levels and the percentage of AFP-L3 in total AFP by the ECLIA and protein microarray. Protein microarray had advantages of smaller sample size required, low cost, and convenience compared with the ECLIA.

Conclusion

The protein microarray assay that was developed in the present study shows potential as an economic and convenient technique for detecting AFP and AFP-L3 levels in serum samples from patients with HCC.

A Quantitative Microtiter Assay for Sialylated Glycoform Analyses Using Lectin Complexes

Fidelity of glycan structures is a key requirement for biotherapeutics, with carbohydrates playing an important role for therapeutic efficacy. Comprehensive glycan profiling techniques such as liquid chromatography (LC) and mass spectrometry (MS), while providing detailed description of glycan structures, require glycan cleavage, labeling, and paradigms to deconvolute the considerable data sets they generate. On the other hand, lectins as probes on microarrays have recently been used in orthogonal approaches for in situ glycoprofiling but require analyte labeling to take advantage of the capabilities of automated microarray readers and data analysis they afford. Herein, we describe a lectin-based microtiter assay (lectin-enzyme-linked immunosorbent assay [ELISA]) to quantify terminal glycan moieties, applicable to in vitro and in-cell glycan-engineered Fc proteins as well as intact IgGs from intravenous immunoglobulin (IVIG), a blood product containing pooled polyvalent IgG antibodies extracted from plasma from healthy human donors. We corroborate our findings with industry-standard LC-MS profiling. This "customizable" ELISA juxtaposes readouts from multiple lectins, focusing on a subset of glycoforms, and provides the ability to discern single- versus dual-arm glycosylation while defining levels of epitopes at sensitivities comparable to MS. Extendable to other biologics, this ELISA can be used stand-alone or complementary to MS for quantitative glycan analysis.

Aleuria Aurantia Lectin (AAL)-reactive immunoglobulin G rapidly appears in sera of animals following antigen exposure

We have discovered an Aleuria Aurantia Lectin (AAL)-reactive immunoglobulin G (IgG) that naturally occurs in the circulation of rabbits and mice, following immune responses induced by various foreign antigens. AAL can specifically bind to fucose moieties on glycoproteins. However, most serum IgGs are poorly bound by AAL unless they are denatured or treated with glycosidase. In this study, using an immunogen-independent AAL-antibody microarray assay that we developed, we detected AAL-reactive IgG in the sera of all animals that had been immunized 1–2 weeks previously with various immunogens with and without adjuvants and developed immunogen-specific responses. All of these animals subsequently developed immunogen-specific immune responses. The kinetics of the production of AAL-reactive IgG in mice and rabbits were distinct from those of the immunogen-specific IgGs elicited in the same animals: they rose and fell within one to two weeks, and peaked between four to seven days after exposure, while immunogen-specific IgGs continued to rise during the same period. Mass spectrometric profiling of the Fc glycoforms of purified AAL-reactive IgGs indicates that these are mainly comprised of IgGs with core-fucosylated and either mono-or non-galactosylated Fc N-glycan structures. Our results suggest that AAL-reactive IgG could be a previously unrecognized IgG subset that is selectively produced at the onset of a humoral response.