Lymphocytes, plasma cells, and mononuclear phagocytes are frequently found in human tissues infected by the Lyme disease spirochete, Borrelia burgdorferi. Experience has shown that these cells comprise the tissue bed inflammatory infiltrate in Lyme disease affecting the joint synovia, myocardium, and skin. While many differences otherwise exist, Lyme synovitis has lymphoplasmacellular similarities with rheumatoid synovitis, lymphoplasmacellular epimyocarditis similarities with syphilitic myocarditis, and occasionally synovial endarteritis obliterans. Silver staining can demonstrate the spirochete if a careful search is done.