Sentence:  Since IL-10 and deficient co-stimulatory molecule expression appear to be a novel mechanism of self-tolerance employed by the pre-naïve B cells, a defect in pre-naïve B-cell functions could lead to a break in self-tolerance, especially in the SLE milieu, where expansion of the pre-naïve B cells has been found [ 3, 4 ], and the immune system is intensely activated as evidenced by elevated B cell-activating factor (BAFF) levels, <WSD>hyperexpression</WSD> of CD40L on T cells, and/or increased levels of certain cytokines such as IL-21 [ 50 – 53 ]. 
Meaning of the word marked with <WSD> tags:  Excessive expression