People with high levels of rheumatoid factor, a marker linked to rheumatoid arthritis, tend to have higher levels of IgM antibodies that react to certain plant proteins called lectins, especially lentil lectin. This pattern suggests a statistical relationship between these immune responses and the presence of rheumatoid arthritis biomarkers.

In people with rheumatoid arthritis, certain antibodies called IgM anti-lectin antibodies tend to appear alongside rheumatoid factor but not alongside anti-nuclear antibodies, suggesting they are linked specifically to rheumatoid arthritis rather than autoimmune conditions in general.

In healthy people, between 12% and 18% have IgM antibodies that bind to plant lectins, and between 9.7% and 16% have IgG or IgA antibodies that bind to these same plant proteins, showing that immune responses to undigested plant components occur in a notable fraction of the population.