Questions: Concept Check 2: Understanding B Cell Activation 1. Antigen-presenting cells - are always macrophages. - are always dendritic cells. - are always phagocytic cells. - present antibody fragments on their surface. - include macrophages, dendritic cells and B cells. 2. All of the following cells have class II MHC receptors on their surface EXCEPT - macrophages. - neutrophils. - red blood cells. - dendritic cells. - B cells. 3. Helper T cells - function in both cell-mediated and humoral immunity. - function in both cell-mediated and innate immunity. - function only in cell-mediated immunity. - function only in humoral immunity by secreting antibodies. - function sometimes in cell-mediated and other times in humoral immunity.

Certainly! Let's address the first three questions from the provided text.

The answer is the last one: include macrophages, dendritic cells, and B cells.

Explanation:

• Are always macrophages: Incorrect. While macrophages are antigen-presenting cells, they are not the only type.
• Are always dendritic cells: Incorrect. Dendritic cells are a type of antigen-presenting cell, but not the only type.
• Are always phagocytic cells: Incorrect. While many antigen-presenting cells are phagocytic, not all are exclusively so.
• Present antibody fragments on their surface: Incorrect. Antigen-presenting cells present antigen fragments, not antibody fragments.
• Include macrophages, dendritic cells, and B cells: Correct. These are the primary types of antigen-presenting cells.

The answer is: red blood cells.

Explanation:

• Macrophages: Incorrect. They do have class II MHC receptors.
• Neutrophils: Incorrect. While not typically known for class II MHC, they are not the exception here.
• Red blood cells: Correct. They do not have class II MHC receptors as they are not involved in antigen presentation.
• Dendritic cells: Incorrect. They have class II MHC receptors.
• B cells: Incorrect. They have class II MHC receptors.

The answer is the first one: function in both cell-mediated and humoral immunity.

Explanation:

• Function in both cell-mediated and humoral immunity: Correct. Helper T cells play a crucial role in both types of immune responses.
• Function in both cell-mediated and innate immunity: Incorrect. They are primarily involved in adaptive immunity.
• Function only in cell-mediated immunity: Incorrect. They also assist in humoral immunity.
• Function only in humoral immunity by secreting antibodies: Incorrect. Helper T cells do not secrete antibodies; they help B cells to do so.
• Function sometimes in cell-mediated and other times in humoral immunity: Incorrect. They function in both simultaneously.

In summary, antigen-presenting cells include macrophages, dendritic cells, and B cells; red blood cells do not have class II MHC receptors; and helper T cells function in both cell-mediated and humoral immunity.