Might this paper be relevant for some of those on Rituximab treatment? It also shows that people with Borrelia infection (i.e. Lyme disease) can show up negative for antibodies to Borrelia, so it is wise not to trust a 'negative' for antibody testing if you have typical symptoms. The authors write: "The sensitivity of B burgdorferi serology in erythema migrans varies from 38 to 88% depending upon the duration of the erythema, which may explain why the patient did not have detectable anti-Borrelia antibodies at that time. Rituximab is known to deplete normal B-lymphocytes and this is likely to have hampered further production of antibodies against B burgdorferi not only in serum, but also in CSF.