Final answer:
The second signal for optimal Naïve CD8+ T cell activation is the engagement of co-stimulatory molecules, which is essential for the T cell to become fully activated and mount an effective immune response.
Step-by-step explanation:
Activation of Naïve CD8+ T cells is critical for a strong cellular immune response. The activation process is three-pronged, often referred to as the three-signal model for optimal T cell activation. The first signal is antigen recognition, where the T-cell receptor (TCR) on the Naïve CD8+ T cells recognizes a processed foreign antigen presented by Major Histocompatibility Complex class I (MHC I) on the surface of an antigen-presenting cell (APC). The second signal involves the engagement of co-stimulatory molecules; these are necessary to prevent anergy in the T cells, which occurs if the TCR is engaged without this second signal. Finally, the third signal is provided by cytokine release, which is essential for T cell proliferation, survival, and differentiation into effector and memory T cells.
In the specified options for Signal 2 of T cell activation, the correct answer is 'b) Co-stimulatory molecules'. These molecules are required to amplify the T cell response initiated by antigen recognition. Without the second signal, the T cell would not become fully activated, potentially leading to an inadequate immune response to the pathogen.