Inbred Strains of Mice Often Generate Highly Polarized CD4 T

Inbred strains of mice often generate highly polarized CD4 T cell responses to specific infections that are dominated by one subset of effector cells. In the case of Balb/c mice infected with the intracellular protozoan Leishmania major, a robust CD4 T cell response is elicited, generating large numbers of L. major-specific T cells; however, this response does not eliminate the pathogen, and instead the mice succumb to the infection. One likely explanation for this finding is:

A) L. major produces immune evasion molecules that prevent pathogen clearance.
B) The antibody response to L. major is too weak to eradicate the pathogen.
C) The CD4 T cell response produces effector cytokines that do not activate macrophages.
D) The CD4 T cells have differentiated into T_H1 instead of T_H2 effector cells.
E) The T_FH cells specific for L. major induce a non-protective class of immunoglobulins.