An enzyme-linked immunosorbent assay for complement regulatory proteins and membrane-bound immunoglobulins on intact red blood cells

Membrane-bound complement regulatory proteins as biomarkers and potential therapeutic targets for SLE

For the last two decades, there had been remarkable advancement in understanding the role of complement regulatory proteins in autoimmune disorders and importance of complement inhibitors as therapeutics. Systemic lupus erythematosus is a prototype of systemic autoimmune disorders. The disease, though rare, is potentially fatal and afflicts women at their reproductive age. It is a complex disease with multiorgan involvement, and each patient presents with a different set of symptoms. The diagnosis is often difficult and is based on the diagnostic criteria set by the American Rheumatology Association. Presence of antinuclear antibodies and more specifically antidouble-stranded DNA indicates SLE. Since the disease is multifactorial and its phenotypes are highly heterogeneous, there is a need to identify multiple noninvasive biomarkers for SLE. Lack of validated biomarkers for SLE disease activity or response to treatment is a barrier to the efficient management of the disease, drug discovery, as well as development of new therapeutics. Recent studies with gene knockout mice have suggested that membrane-bound complement regulatory proteins (CRPs) may critically determine the sensitivity of host tissues to complement injury in autoimmune and inflammatory disorders. Case-controlled and followup studies carried out in our laboratory suggest an intimate relation between the level of DAF, MCP, CR1, and CD59 transcripts and the disease activity in SLE. Based on comparative evaluation of our data on these four membrane-bound complement regulatory proteins, we envisaged CR1 and MCP transcripts as putative noninvasive disease activity markers and the respective proteins as therapeutic targets for SLE. Following is a brief appraisal on membrane-bound complement regulatory proteins DAF, MCP, CR1, and CD59 as biomarkers and therapeutic targets for SLE.

Band 3 clustering promotes the exposure of neoantigens in Plasmodium falciparum-infected erythrocytes

Erythrocytes infected with the human malaria parasite Plasmodium falciparum become structurally and antigenically modified as a consequence of intracellular parasite development. The new antigens that appear on the surface of the infected erythrocyte originate from parasite-encoded proteins and by modification of the erythrocyte membrane protein band 3. Here, we show that anti-peptide antibodies generated against an amino acid sequence (YETFSKLIKIFQDH) of human band 3, and previously identified as mediating adhesion of infected erythrocytes to CD36, recognized P. falciparum-infected erythrocytes. In addition, sera from individuals living in a malaria endemic area (and who are presumably immune) contained immunoglobulins specific for this region of band 3. The anti-peptide antibodies reacted with the surface excrescences (knobs) on falciparum-infected erythrocytes. In uninfected erythrocytes, the band 3 region was cryptic and its exposure on the falciparum-infected erythrocyte surface required clustering of band 3 protein. Thus, a parasite-induced modification of band 3 promotes adhesion and induces antigenic changes in the P. falciparum-infected erythrocyte.

Reduction in erythrocyte complement receptor 1 (CR1, CD35) and decay accelerating factor (DAF, CD55) during normal pregnancy

RBC-membrane CR1 has been assayed in pregnancy and at 48 h postpartum. It has been shown that RBC CR1 is reduced as pregnancy progress, reaching a nadir in the third trimester and that it returns to levels approaching normal within 48 h postpartum. Further, there is a reduced expression of RBC decay accelerating factor (DAF) during pregnancy but no change in expression of RBC CD59. We suggest that the reduction in RBC CR1 and DAF may reflect increased levels of circulating immune complexes and consequent increased complement activation in pregnancy.

Do plasma anti phospholipid antibodies in patients with autoimmune haemolytic anaemia correlate with reduced levels of erythrocyte complement receptor 1?

Anti phospholipid antibody (APA), of both IgG and IgM class, was assayed in plasma obtained from patients with autoimmune haemolytic anaemia (AHA) and active haemolysis. Although plasma APA was elevated in some AHA patients, when compared to a normal control population, there was no apparent correlation with levels of erythrocyte complement receptor 1 (RBC-membrane CR1) in this patient group. However, there appeared to be a correlation between RBC-membrane CR1 and plasma IgG APA in a subset of the AHA patients with low RBC-membrane CR1. The potential significance of this observation was complicated by the majority of these patients having a plasma APA within the normal range. These results suggest that the reported inverse correlation between APA and RBC-membrane CR1 may not be definitive.