IMD Berlin doesn't measure large values, they are looking for a deficiency. Doctors are telling me that high values don't have any significance. They don't seem to be up-to-date. I also did hyposensitization therapy in the past and could have bumped it up. It's either that there are more IgG4+ plasma B-cells present or normal plasma B-cell count with increased IgG4 secretion. To answer your question: I don't know and healthcare doesn't investigate.
MBL2 status seems related to disease severity per this study and some earler ones.
"The present study was designed to conduct a systematic investigation of the interaction of the human humoral PRMs with SARS-CoV-2. We found that PTX3 and MBL bound the SARS-CoV-2 nucleocapsid protein and spike protein, respectively. MBL recognized VoC, had antiviral activity and activated the complement lectin pathway. Genetic polymorphisms at the MBL2 locus were associated with disease severity. Thus, selected fluid-phase PRMs (ante-antibodies) play an essential role in resistance to and pathogenesis of COVID-19, a finding with translational implications."
I think this study relative to optimal MBL blood level for longevity is a good summary of the effect of MBL:
either too few or too much are deleterious!
Activity of mannose-binding lectin in centenarians
We analyzed MBL2 gene variants in two cohorts of centenarians, octo-nonagenarians and nonagenarians, and in the general population, one from Sardinia Island (Italy), recruited in the frame of the AKea study, and another from Campania (southern Italy), to search for haplotypes related to longevity. We also assessed in vitro the effect of mannose-binding lectin (MBL) on various human cells at different stage of senescence.
The frequency of high and null activity haplotypes was significantly lower, and the frequency of intermediate activity haplotype significantly higher in centenarians and in subjects between 80 and 99 years from both the cohorts as compared each to the general population from the same geographic area.
Furthermore, serum MBL concentration (also after normalization to serum albumin) was significantly lower in centenarians and in octo- and nonagenarians as compared to the general population, suggesting that intermediate MBL haplotype/activity may be protective.
We also demonstrated that in vitro MBL protein bound to senescent IMR90 fibroblasts thereby causing cell lysis, but not to other types of cycle-arrested cells not in senescence.
This implicates a novel role of MBL in the clearance of senescent cells.