Detection and activation of HIV broadly neutralizing antibody precursor B cells using anti-idiotypes

Bancroft, Tara; DeBuysscher, Blair L.; Weidle, Connor; Schwartz, Allison; Wall, Abigail; Gray, Matthew D.; Feng, Junli; Steach, Holly R.; Fitzpatrick, Kristin S.; Gewe, Mesfin M.; Skog, Patrick D.; Doyle-Cooper, Colleen; Ota, Takayuki; Strong, Roland K.; Nemazee, David; Pancera, Marie; Stamatatos, Leonidas; McGuire, Andrew T.; Taylor, Justin J.

Previous studies have shown that autoreactive B cells that escape deletion are often rendered functionally unresponsive to antigenic stimulation, a state referred to as anergy (Goodnow et al., 1988 Cyster et al., 1994; Fulcher and Basten, 1994; Klinman, 1996; Nemazee, 2006 Nemazee, , 2017 . Given this, we next considered whether the B cells remaining in iglb12 heavy chain transgenic mice were anergic. Previously, several phenotypes of anergic B cells have been described in mice, including CD93 + CD23 + IgM LOW "T3" transitional phenotype, as well as mature B cells expressing low levels of IgM (Allman et al., 2001; Merrell et al., 2006; Taylor et al., 2012; Agrawal et al., 2013; Sabouri et al., 2016) . In agreement with the hypothesis that circulating iglb12 heavy chain transgenic B cells were anergic, the number of T3 cells was increased 29-fold in these animals compared with control transgenic animals (Fig. 6 , C and E). In addition, IgM expression was 6.4-fold lower on mature B cells from iglb12 heavy chain transgenic mice compared with control heavy chain transgenic animals (Fig. 7 A) . IgD expression was also reduced 1.9-fold on mature B cells from iglb12 heavy chain transgenic mice compared with control transgenic animals ( Fig. 7 B) , which suggested a global down-regulation of surface BCR on these cells. Down-regulated surface BCR expression by iglb12 heavy chain transgenic mature B cells was confirmed through the assessment of CD79β (Igβ; Fig. 7 C) , a component of the BCR signaling complex required for surface BCR expression.