Polyclonal B cell activation in infections: infectious agents' devilry or defense mechanism of the host?

Polyclonal B cell activation is not a peculiar characteristic to a particular infection, as many viruses, bacteria, and parasites induce a strong polyclonal B cell response resulting in hyper-gamma-globulinemia. Here, we discuss the different roles proposed for polyclonal B cell activation, which can be crucial for early host defense against rapidly dividing microorganisms by contributing antibodies specific for a spectrum of conserved structures present in the pathogens. In addition, polyclonal B cell activation can be responsible for maintenance of memory B cell responses because of the continuous, unrestricted stimulation of memory B cells whose antibody production may be sustained in the absence of the antigens binding-specific BCR. Conversely, polyclonal activation can be triggered by microorganisms to avoid the host-specific, immune response by activating B cell clones, which produce nonmicroorganism-specific antibodies. Finally, some reports suggest a deleterious role for polyclonal activation, arguing that it could potentially turn on anti-self-responses and lead to autoimmune manifestations during chronic infections.