CD6 deficiency impairs early immune response to bacterial sepsis

CD6 is a lymphocyte-specific scavenger receptor expressed on adaptive (T) and innate (B1a, NK) immune cells, which is involved in both fine-tuning of lymphocyte activation/differentiation and recognition of bacterial-associated molecular patterns (i.e., lipopolysaccharide). However, evidence on CD6's role in the physiological response to bacterial infection was missing. Our results show that induction of monobacterial and polymicrobial sepsis in Cd6 ^-/- mice results in lower survival rates and increased bacterial loads and pro-inflammatory cytokine levels. Steady state analyses of Cd6 ^-/- mice show decreased levels of natural polyreactive antibodies, concomitant with decreased cell counts of spleen B1a and marginal zone B cells. Adoptive transfer of wild-type B cells and mouse serum, as well as a polyreactive monoclonal antibody improve Cd6 ^-/- mouse survival rates post-sepsis. These findings support a nonredundant role for CD6 in the early response against bacterial infection, through homeostatic expansion and functionality of innate-related immune cells.