This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
In a patient with a Salmonella infection, which of the following mechanisms will most likely be the earliest adaptive response for clearing the infection while bacteria are present within intracellular endosomes? 
Select and explain. 
A. Antibody mediated neutralization of free bacteria, B. Complement mediated lysis of infected host cells, C. CTL recognition of bacterial peptides presented by MHC class II, D. DTH responses generated by CD4 +T cells
D: DTH responses generated by CD4 +T cells
Answer: D: DTH responses generated by CD4 +T cells 
Explanation: Ans. (d)DTH responses are generally the first effective responses involved in clearance of intraendosomal microbes. Later in such infections, the microbes or their molecules may escape into the cytoplasm, making it possible for Cytotoxic T lymphocyte responses to develop. Complement does not clear active intracellular infections. Antibodies maybe effective in inhibiting reinfection but do not cleat active intracellular infections.