Indicate the true statements and correct the false statements so they are true.
a. B cells are activated by antigen-presenting cells
b. T cytotoxic cells are activated by antigens bound to MHC I
c. Upon activation, T helper cells stimulate T cytotoxic cells and B cells
d. IgG is the first antibody made during a primary response
e. T-dependent antigens rely on TH cells to activate B cells

Verified step by step guidance

1. Step 1: Analyze statement (a): Understand that B cells can be activated directly by antigens binding to their receptors, but they often require help from antigen-presenting cells (APCs) such as dendritic cells or macrophages to present processed antigen fragments. Clarify whether the statement implies direct activation or activation with APC involvement, and correct it if necessary.
2. Step 2: Examine statement (b): Recall that T cytotoxic (CD8+) cells recognize antigens presented on MHC class I molecules. Confirm that this statement is true as it aligns with the fundamental immunology principle of antigen presentation to cytotoxic T cells.
3. Step 3: Review statement (c): Understand that upon activation, T helper (CD4+) cells secrete cytokines that stimulate both T cytotoxic cells and B cells. Verify that this statement is true based on the role of T helper cells in adaptive immunity.
4. Step 4: Evaluate statement (d): Remember that IgM is typically the first antibody produced during a primary immune response, not IgG. Correct the statement by replacing IgG with IgM to make it true.
5. Step 5: Assess statement (e): Recognize that T-dependent antigens require the assistance of T helper cells to activate B cells, which is a true statement. Confirm this understanding and leave the statement as is.

Key Concepts

Activation of B Cells

B cells are activated primarily by direct binding to their specific antigen through the B cell receptor. While antigen-presenting cells (APCs) like dendritic cells activate T cells, B cells require antigen recognition and often help from T helper cells for full activation, especially in T-dependent responses.

Role of MHC I in T Cytotoxic Cell Activation

T cytotoxic (CD8+) cells recognize antigens presented on MHC class I molecules, which are found on all nucleated cells. This presentation allows cytotoxic T cells to identify and kill infected or abnormal cells displaying intracellular antigens.

Antibody Response and Immunoglobulin Classes

During a primary immune response, IgM is the first antibody produced, followed by class switching to other types like IgG. IgG is the most abundant antibody in secondary responses and provides long-term immunity.