Play(s) an important role in both humoral and cell-mediated immunity.
a. killer cytotoxic (cd8+) t cells
b. neutrophils
c. b lymphocytes
d. t cells (cd4+)
e. all of the above play an important role in both humoral and cell-mediated immunity

d. Helper T cells (CD4+)

Explanation:

There are two kinds of immune responses, innate and adaptative (humoral and cell-mediated):

Cell-mediated immunity (CMI) refers to protective mechanisms that are not characterized by antibody, this kind of immunity is responsible for detecting and destroying intracellular pathogens, tumor cells and delayed-type hypersensitivity reactions. This CMI is mediated by lymphocytes T, T helpers identifying endogenous antigens and stimulating Killer cytotoxic (CD8+) T cells that liberate perforating enzymes into the infected cells causing lysis.

Humoral immunity describes the kind of immunity in which antibodies are produced by B lymphocytes to target exogenous antigens. In this kind of response Helper T cells also play a role secreting cytokines to activate the appropriate B lymphocyte.

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