There Is No Single Accepted Measure of Immunocompetence at the Present

There is no single accepted measure of immunocompetence at the present time.One reason is that

A) the natural killer cells are very effective but difficult to measure
B) immunosuppression is easier to measure
C) there are individual differences between people in ways of responding to stress
D) ineffective cell measurement tools exist
E) until now there has been very little interest in immunocompetence