**Core Concept**
MHC (Major Histocompatibility Complex) class II molecules are crucial for the presentation of antigens to T helper cells (CD4+ T cells) in the context of an immune response. They are primarily expressed on the surface of antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells. The presentation of antigens by MHC II molecules is essential for the activation and regulation of the adaptive immune response.

**Why the Correct Answer is Right**
MHC II molecules are not expressed on the surface of neurons. This is because neurons do not typically engage in antigen presentation and are generally not involved in the adaptive immune response. The lack of MHC II expression on neurons helps to maintain the delicate balance between the nervous and immune systems, preventing potential autoimmune responses against self-antigens. In contrast, MHC II molecules are abundantly expressed on the surface of APCs, where they play a pivotal role in the initiation of an immune response.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** This option is not provided.
**Option C:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that MHC II molecules are not expressed on the surface of neurons, which helps to prevent autoimmune responses against the nervous system.

**Correct Answer:** A.