MRCP2-2743

A 45-year-old man has been experiencing confusion and decreased mental function, as well as loss of coordination and movement in his right arm for the past six weeks. An MRI scan has revealed lesions in the white matter and grey-white junction of his cerebral hemispheres, indicating demyelination. A stereotactic biopsy was performed, and immunohistochemical staining of the tissue showed the presence of JC papovavirus in oligodendrocytes. Which of the following laboratory test results is most likely to be associated with these findings?