Expression of (A) FAP, (B) podoplanin, (C) CD248, (D) CD55 were measured by pixel counting in synovial regions of interest in uninflamed tissue of patients with mechanical joint symptoms undergoing exploratory arthroscopy (Control), and in baseline samples of early arthritis patients, split into patients fulfilling ACR/EULAR 2010 criteria for RA during follow-up (very early rheumatoid arthritis; VERA) and combined non-RA groups made up of patients with spontaneously resolving arthritis and patients with non-RA persistent arthritis (NON-RA). (A) FAP expression was higher in VERA patients (n = 32) compared to other outcome groups (n = 24) (Kruskal-Wallis p = 0.0036, asterisks denote the results of Dunn’s post-test, *p<0.05). Red data points indicate the subgroup of patients developing seronegative, persistent RA. (B) Podoplanin expression also differed between outcome groups (Kruskal-Wallis p = 0.0062), but there was no significant difference in post-testing between VERA (n = 29) and NON-RA groups (n = 23). (C,D) No significant difference was observed in CD55 (lining; 21 VERA vs 13 non-RA) or CD248 (sublining; 16 VERA vs 8 non-RA) expression. Each dot represents a patient; median bars with interquartile ranges are shown.