A group from University of Cambridge, Cambridge, United Kingdom, etc. has reported on importance of lectin complement pathway on severe COVID-19 pathology.
https://www.frontiersin.org/articles/10.3389/fimmu.2021.714511/full
The complement system is an integral part of the innate and the adaptive immune systems, and three pathways are known: Classical pathway, Alternative pathway, and Lectin pathway.
The mannan-binding lectin-associated serine protease-2 (MASP-2) is the key enzyme of the Lectin pathway. The activated MASP-2 can cleave C4 efficiently to form C3 and C5 convertase complexes C4bC2a and C4bC2aC3b, leading to the formation of membrane attack complex (MAC). The pathogen-associated molecular patterns (PAMPs) recognition subcomponents (LP recognition molecules) are the key to activate MAPS-2. Those in humans are mannose-binding lectin (MBL), collectin-11 (CL-11), and heterocomplexes of CL-11 and CL-10 and ficolin. The Lectin pathway is initiated by the complexes of LP recognition subcomponent and MAPS-2 bind to PAMPs.
Binding of LP recognition molecules to SARS-CoV-2 proteins was studied. A MTP ELISA plate was coated with either SARS-CoV-2 Spike, SARS-CoV-2 N protein or control ligands (mannan for MBL, N-acetyl BSA for ficolin 2(FCN2), zymosan for CL-11), and serial dilutions of serum were added to the wells. It is clearly shown that LP recognition molecules such as MBL, ficolin2, and CL-11 bind to SARS-CoV-2 Proteins.
Although it was not mentioned if the LP was associated with COVID-19 severity in this report, this might be one of causes leading to acute respiratory distress syndrome (ARDS).