Antigen-presenting cells are key in naïve T cell activation. APCs will circulate the body, gathering up pieces of foreign cells in the form of antigens and carrying them back to the SLOs.
Once the APC comes in contact with a T cell expressing the corresponding TCR, the antigen-MHC complex will bind to the TCR and initiate the signaling cascade. This alone is not sufficient to activate most naïve cells and can cause a cell to become anergic, or unable to carry out an immune response.
To successfully catalyze an inflammatory reaction and achieve naïve cell activation and expansion, three binding signals must occur at the same time: TCR binding, cytokine signaling, and the binding of a co-stimulatory molecule, such as CD28.
Cytokines and co-stimulatory molecules bolster the effects of TCR binding to the antigen in order to trigger an activation cascade. Once naïve cells are activated by the APC, the cells differentiate into effector cells and begin the process of nullifying the potential infection.
Antibody Synthesizing Capabilities
B cells can be activated by direct binding to an antigen. Once a naive B cell recognizes its target antigen, they form germinal centers with the help of CD4  helper T cells.
In the germinal center early stage antibody-secreting B cells undergo isotype switching and transition into a plasma cell. Antibody production by B cells can quickly neutralize a potential infection. Once the infection is neutralized, B cells can become memory B cells, which exist in small numbers in the case of re-infection.