Effector cells are a type of cell in the body that carry out a specific activity in response to stimulation. In the immune system, effector cells are activated cells that protect the body by providing a specific response against the invading pathogen. 

There are two main types of effector cells - TH1 and TH2. Each has a different function in the immune system.

• TH1 Effector Cells serve multiple functions all of which help to defend the body. They are involved in fighting off viral infections, suppressing inflammation, and playing a role in delayed hypersensitivity. TH1 effector cells also secrete interferon-gamma, which inhibits the expansion of TH2 effector cells and produce IL-2, which facilitates the differentiation of T cells into CTL. 
• TH2 Effector Cells- play a role in activating eosinophil, mediating IgM class switching to IgG, and suppressing the clonal expansion of TH1 effector cells. They are also involved in the proliferation, activation and differentiation of B cells.