IgM antibodies to oxidized phosphatidylserine as protection markers in cardiovascular disease among 60-year olds.

Objective: Phosphatidylserine is exposed on apoptotic cells and is prone to oxidation (OxPS). Here we analyze the association of IgM antibodies against OxPS (anti-OxPS) with the risk of cardiovascular disease (CVD).
Methods: Among sixty-year olds from Stockholm County in Sweden, previously screened for cardiovascular risk factors (2039 men, 2193 women), there were 210 incident CVD-cases identified during a 5-year follow-up. Using a nested case-control design, 622 age- and sex-matched controls were selected. Odds ratios (OR) with 95% intervals (CI) were calculated by conditional logistic regression. IgM anti-OxPS was measured by ELISA. Phagocytosis of apoptotic Jurkat-cells by macrophages was studied by flow cytometry.
Results: Anti-OxPS levels were lower among cases (median (interquartile range): 80.7 (60.9-101.0 vs. 84.6 (65.8-109.6); p = 0.047); among men (76.6 (55.8-99.2) vs. 82.0 (63.1-105.1); p = 0.022) and among women 89.6 (72.3-110.1) vs. 89.8 (69.9-114.4); p = 0.79). After adjustment for smoking, BMI, diabetes mellitus type II, hypercholesterolaemia and hypertension, and dividing into quartiles, using the highest quartile (quartile 4) as reference, quartile 3 was associated with a OR of 1.74 (CI 1.08-2.81). Quartiles 2 and 1 had similar associations, the later reaching statistical significance. Among men associations were stronger whereas no significant associations were observed in women. The OR of MI/angina comparing quartile 3 with quartile 4 was 2.31 (CI 1.30-4.11). The OR for quartile 2 and 1, respectively, were similar as for quartile 3. Total IgM increased uptake of apoptotic cells, which was reversed if incubated with OxPS.
Conclusions: IgM anti-OxPS is a novel potential protection marker for CVD, in particular in men. Increased phagocytosis of dying/dead cells could be one potential underlying mechanism.