The doubtful results of the ELISA test were observed only for B. burgdorferi s.l. In MS patients the doubtful results were 0.8% (1/124) and 3.2% (4/124) for IgM and IgG tests, respectively, whereas the doubtful results for this pathogen were not noted in blood donors. Here, CD40LG is linked to myeloid sarcoma.