Polymerized type I collagen down-regulates STAT-1 phosphorylation through engagement to LAIR-1 in M1-macrophages avoiding long COVID

Background The polymerized type I collagen (PTIC) is a γ-irradiated mixture of pepsinized porcine type I collagen and polyvinylpyrrolidone (PVP). It has immunomodulatory properties. However, the receptor and signaling pathway through which it exerts its therapeutic effects has not yet been identified. Aim To evaluate LAIR-1 as a potential receptor for PTIC and the signaling pathway evoked by ligand-receptor binding. Methods LAIR-1 binding assay was performed by incubating various concentrations of recombinant human LAIR-1 with native type I collagen or PTIC. Macrophages M1- derived from THP-1 cells were cultured with 2-10% PTIC for 24 h. Cell lysates from THP- 1, monocytes-like cells (MLCs), M1, M1+IFN-γ, M1+LPS, and 2 or 10% PTIC treated M1 were analyzed by western blot for the transcription factors NF-κB (p65), p38, STAT-1, and pSTAT-1. Cytokines, Th1 cells, and M1/M2 macrophages were analyzed by luminometry and flow cytometry from blood samples of symptomatic COVID-19 outpatients on treatment with intramuscular administration of PTIC. Results PTIC binds LAIR-1 with a similar affinity to native collagen. This binding decreases STAT-1 signaling IFN-γ-induced and IL-1β expression in M1 macrophages by down-regulating STAT-1 phosphorylation. Moreover, intramuscular PTIC treatment of symptomatic COVID-19 outpatients decreased at statistically significant levels the percentage of M1 macrophages and cytokines (IP-10, MIF, eotaxin, IL-8, IL-1RA, and M- CSF) associated with STAT-1 transcription factor and increased M2 macrophages and Th1 cells. The downregulation of inflammatory mediators was related to better oxygen saturation and decreased dyspnea, chest pain, cough, and chronic fatigue syndrome in the acute phase of infection and the long term. Conclusion PTIC is an agonist of LAIR-1 and down-regulates STAT-1 phosphorylation. PTIC could be relevant for treating STAT-1-mediated inflammatory diseases, including COVID-19 and long COVID ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial NCT04517162 ### Funding Statement Polymerized type I collagen and type I collagen were donated by Aspid SA de CV. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Institutional review board of the Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran (INCMNSZ, reference no. IRE 3412-20-21-1) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors