Strenuous muscular is just a fancy way to say exercise. As the muscles are used more often the need more oxygen, so that is why your breathing rate increases while doing "exercise".
FCRL4 is a type of immunoregulatory receptor. It is expressed by memory B cells (MBCs) localized in sub-epithelial regions of lymphoid tissues. Both FCRL4 and Glutathione function as pro-inflammatory for b-cells and t-cells respectively during the event of autoimmune disease responses.
