NK‐cell exhaustion, B‐cell exhaustion and T‐cell exhaustion—the differences and similarities

T-cell exhaustion has been extensively researched, compared with B-cell exhaustion and NK-cell exhaustion, which have received considerably less attention; and there is less of a consensus on the precise definitions of NK-cell and B-cell exhaustion. NK-cell exhaustion, B-cell exhaustion and T-cell exhaustion are examples of lymphocyte exhaustion, and they have several differences and similarities. Lymphocyte exhaustion is also frequently confused with anergy, cellular senescence and suppression, because these conditions can have significant overlapping similarities with exhaustion. An additional source of confusion is due to the fact that lymphocyte exhaustion is not a binary state, but instead has a spectrum of severity induced by different levels and duration of continuous antigenic stimulation. Concurrent multiple types of lymphocyte exhaustion are possible, and this situation is herein called poly-lymphocyte exhaustion. Poly-lymphocyte exhaustion for the same cancer or pathogen would be especially dangerous. As there are significant advantages for a pathogen by inducing poly-lymphocyte exhaustion in an immune system, there are pathogens with an evolved capability to induce poly-lymphocyte exhaustion. These pathogens may include certain manipulative viruses, bacteria, fungi and protozoan parasites.