Levels of inflammatory factors such as interleukin 6 (IL-6) and serum amyloid A (SAA) are distinctly elevated in severe cases of coronavirus disease 2019. A role in regulation of such factors could be attributed to autoantibodies against them. The aim of our research was to determine the values of autoantibodies against IL-6 and against SAA in sera samples of healthy blood donors and coronavirus disease 2019 patients and to analyze these values.
To determine the values of antibodies against IL-6 we set up and validated a new in-house ELISA. We determined the needed parameters for the adequate precision of the method and verified the specificity by fluid phase and solid phase inhibition.
In the healthy blood donors’ group, we noticed that gender and age of an individual don’t influence the value of the antibodies against IL-6 and SAA. There was no significant difference in the levels of antibodies against SAA between the two groups, but the patients had significantly higher values of antibodies against IL-6 compared to blood donors (p = 0,0018). The higher levels of those antibodies among patients suggest that the antibodies might form complexes with IL-6, that could prolong their half-life in the circulation. We also checked for correlations among the examined factors and observed the significant correlation between antibodies against IL-6 and against SAA in both groups. We also noticed a significant correlation between IL-6 and antibodies against SAA.
To see how the values of the examined antibodies change during the disease we chose the samples of some of the patients for longitudinal observation. The levels of the examined antibodies mostly decreased during the time of hospitalization.
We also checked the neutralizing ability of the antibodies against SAA with functional tests on cells. The used sera have non-specifically inhibited SAA, but there was no neutralizing ability to be observed with isolated IgG fractions.