In multiple sclerosis (MS), B cell-depleting therapy using monoclonal anti-CD20 
Abs, including rituximab (RTX) and ocrelizumab, effectively reduces disease 
activity. Based on indirect evidence, it is generally believed that elimination 
of the Ag-presenting capabilities and Ag nonspecific immune functions of B cells 
underlie the therapeutic efficacy. However, a small subset of T lymphocytes (T 
cells) was shown to also express CD20, but controversy prevails surrounding the 
true existence of this T cell subpopulation. Using single-cell imaging flow 
cytometry and expression profiling of sorted lymphocyte subsets, we 
unequivocally demonstrate the existence of CD3(+)CD20(dim) T cells. We show that 
in MS patients, increased levels of CD3(+)CD20(dim) T cells are effectively 
depleted by RTX. The pathological relevance of this T cell subset in MS remains 
to be determined. However, given their potential proinflammatory functionality, 
depletion of CD20-expressing T cells may also contribute to the therapeutic 
effect of RTX and other mAbs targeting CD20.