Autoantibodies with a protective function: polyreactive antibodies against alkaline phosphatase in bacterial infections

Impact of Unconjugated estriol (uE3) assay interference on prenatal screening tests

BACKGROUND

Unconjugated estriol (uE3) is an important biomarker in second trimester prenatal screening. Previous studies from our laboratory identified rare interference in the Beckman uE3 assay due to anti-ALP antibodies, which could be mitigated with a scavenger or heat-inactivated ALP (hALP). In the current study, 160 de-identified patient samples previously submitted for the Quad screen with low uE3 multiples of the median (MoM ≤0.50) were investigated for potential interference.

METHODS

A reagent pack spiking strategy with hALP was employed to understand if the interference could be identified and mitigated in a scalable manner. The 160 samples were measured using uE3 lot #920861 previously known to be subject to interference, lot #920861 spiked with hALP, and the vendor reformulated lot #922579. Samples were suspected to have interference if the percent difference in uE3 measurements was >50%. Pseudo-risks were calculated using a test patient environment to understand the screening impact due to the change in uE3 result.

RESULTS

Seventeen of the 160 samples had uE3 results that were >50% different between the hALP spiked and non-spiked reagent pack. Both original lot #920861 with hALP and reformulated lot #922579 identified the same 17 patients as having interference in lot #920861. Analysis of screening risks using a test patient environment showed that assay interference could result in false positives for one trisomy 21 and three trisomy 18 post-test risk calculations.

CONCLUSION

Our experiment of reagent pack spiking with hALP produced similar uE3 results to a reformulated reagent designed to address potential interference, demonstrating that this is a feasible strategy to screen for interference in a scalable manner. The vendor-provided reformulation addressed anti-ALP interference and improved the performance of the screen.

Detection and characterization of estradiol (E2) and unconjugated estriol (uE3) immunoassay interference due to anti-bovine alkaline phosphatase (ALP) antibodies

Objectives

Competitive immunoenyzmatic assays for estradiol (E2) and unconjugated estriol (uE3) on UniCel DxI 800 Access immunoassay systems (Beckman Coulter) utilize bovine alkaline phosphatase (ALP) for amplification. In these assays, rare 'IND' error flags indicate that a relative light unit (RLU) raw result is past the high or low end of the calibration curve but cannot be differentiated from an instrument error or analytical interference. The present studies were conducted to establish a protocol to identify analytical interference and to characterize its mechanism when present.

Design and methods

Matrix and recovery studies were conducted to establish a protocol for interference identification. Spiking experiments with inactivated calf intestinal ALP were performed to determine whether interference could be blocked. Commercial anti-ALP antibodies (Abs) were spiked into human serum to model assay interference. Three E2 immunoassays which do not include ALP as a reagent component (cobas e602, Roche; Centaur XP, Siemens; ARCHITECT i2000_SR, Abbott) were tested for comparative purposes.

Results

1:2 dilution of specimen into Access Sample Diluent A (Beckman) differentiated IND error flags due to true low results (e.g. less than the analytical measurement range; AMR) from those due to assay interference. Interferences were reduced by pre-incubation with inactivated ALP and could be replicated by spiking with commercial anti-ALP Abs.

Conclusions

Patient anti-bovine ALP Abs can cause interference on DxI 800 E2 and uE3 assays. This model can be used to investigate interference risk with other ALP-dependent assays.

An alkaline phosphatase transport mechanism in the pathogenesis of Alzheimer's disease and neurodegeneration

Systemic inflammation is associated with loss of blood-brain barrier integrity and neuroinflammation that lead to the exacerbation of neurodegenerative diseases. It is also associated specifically with the characteristic amyloid-β and tau pathologies of Alzheimer's disease. We have previously proposed an immunosurveillance mechanism for epithelial barriers involving negative feedback-regulated alkaline phosphatase transcytosis as an acute phase anti-inflammatory response that hangs in the balance between the resolution and the progression of inflammation. We now extend this model to endothelial barriers, particularly the blood-brain barrier, and present a literature-supported mechanistic explanation for Alzheimer's disease pathology with this system at its foundation. In this mechanism, a switch in the role of alkaline phosphatase from its baseline duties to a stopgap anti-inflammatory function results in the loss of alkaline phosphatase from cell membranes into circulation, thereby decreasing blood-brain barrier integrity and functionality. This occurs with impairment of both amyloid-β efflux and tau dephosphorylating activity in the brain as alkaline phosphatase is replenished at the barrier by receptor-mediated transport. We suggest systemic alkaline phosphatase administration as a potential therapy for the resolution of inflammation and the prevention of Alzheimer's disease pathology as well as that of other inflammation-related neurodegenerative diseases.

Evidence for polyreactive xenoreactive antibodies in the repertoire of human anti-swine antibodies: the 'next' humoral barrier to xenotransplantation?

The xenoreactive nature of anti-Galalpha1-3Gal antibodies, and to a lesser extent, polyreactive antibodies, has been characterized by a number of investigators. With the advent of therapies that avoid hyperacute xenograft rejection due to anti-Galalpha1-3Gal antibodies coupled with the possible development of Galalpha1-3Gal deficient swine, the Galalpha1-3Gal antigen may soon cease to be a barrier to xenotransplantation. With this in mind, the potential xenoreactive nature of polyreactive antibodies was investigated using several approaches. The levels of polyreactive antibodies from the serum of newborn (n = 2) and adult (n = 4) baboons undergoing pulmonary xenotransplantation were evaluated. Depletion of 95% and 94% of total serum IgM, without any decrease in albumin levels, was observed in the newborn baboons. This finding indicates that the IgM present at birth and germ line polyreactive IgM was adsorbed by the xenografts. The depletion of polyreactive antibodies (43-83% reduction of anti-DNP IgM) from adult baboons was also observed following pulmonary xenotransplantation or immunoadsorption therapy plus pulmonary xenotransplantation. Additional experiments using human cord serum indicated that most human polyreactive IgM were adsorbed by pig lung homogenate and that the human polyreactive IgM bound approximately two-fold more to immobilized pig lung antigens than to immobilized human lung antigens. These findings indicate that germline polyreactive antibodies are, for the most part, xenoreactive. These data suggest that polyreactive antibodies, although autoreactive, may be more xenoreactive than autoreactive.

Immunosuppression without immunosuppression? How to be a tolerant individual in a dangerous world

The field of transplantation has developed based on two principles: allografts are rejected because they express foreign antigens, and the immune system must be suppressed to prevent rejection. Recently, in vitro and in vivo experimental evidence has accumulated that calls both of these beliefs into question. This article reviews an alternative approach to transplantation that focuses on tissue injury as the instigator of graft rejection and employs physiological mechanisms of tolerance to avoid graft loss. Methods that allow for defense against infectious microbes while at the same time allowing for graft survival are proposed. In particular, the rationale behind the use of anti-CD154 antibody treatment is highlighted. A model is introduced that takes into consideration the experimental successes seen with anti-CD154 therapies.