Agranular leukocytes include monocytes and lymphocytes. Lymphocytes are B cells, T cells and NK cells. Granular leukocytes are neutrophil, eosinophils and basophils. Monocytes and macrophage are now known to contain cytoplasmic granules, but they just don't show up very well under the microscope. The inactive complement proteins are present is serum all the time.
Complement activation takes at the site of the infection.
This is the place where cell surfaces will be around to activate complement by the alternative pathway, and where antibodies bound to antigen are present for activation via the classical pathway. T helper cells differentiate to Memory cells and effector cells. This is opposed to memory cells which just hang out and wait for an addition exposure to the antigen.