What is the Difference Between T Cell Dependent and Independent Antigens

The main difference between T cell-dependent and independent antigens is that T cell-dependent antigens require the help of T cells for the activation of B cells. In contrast, T cell-independent antigens do not need the help of T cells for the activation of B cells.

n brief, T-cell dependent and independent antigens are two types of antigens that elicit B-cell response. The activation of B cells may or may not require the help of T cells.  

Key Areas Covered

1. What are T Cell Dependent Antigens
     – Definition, Features, Importance
2. What are T Cell Independent Antigens
     – Definition, Features, Importance
3. Similarities Between T Cell Dependent and Independent Antigens
     – Outline of Common Features
4. Difference Between T Cell Dependent and Independent Antigens
     – Comparison of Key Differences

Key Terms

T Cell Dependent Antigens, T Cell Independent Antigens

What are T Cell Dependent Antigens

T-cell dependent antigens are the type of antigens that require the help of T cells for the activation of B cells. The majority of T-cell dependent antigens are proteins. They first bind to the mIg on B cells and are internalized by receptor-mediated endocytosis or pinocytosis that is non-specific. These internalized proteins undergo processing by peptidase enzymes in lysosomes, generating peptide fragments that bind to MHC class II molecules. Then, peptide-MHC complexes emerge on the cell surface of B cells, interacting with T cell receptors (TCRs) on helper T cells. Moreover, this release cytokines, directing B-cell proliferation and maturation.

Figure 1: T-Dependent B Cell Activation

Furthermore, the activated B cells differentiate into plasma B cells that produce antibodies.

What are T Cell Independent Antigens

T cell-independent antigens are antigens that do not require the help of T cells for B cell activation. They are polymeric molecules containing repeating units of antigenic determinants. Therefore, they are multivalent antigens. For example, polysaccharides and polymeric proteins in microorganisms are T-independent polymeric antigens.

Figure 2: T-Independent B Cell Activation

Moreover, T-independent antigens cross-link surface receptors of B cells. This tends to produce antigens in B cells by B cell activation. However, without the help of helper T cells, B cells do not produce immunoglobulin isotypes, and therefore, the only form of antibodies produced by B cells is IgM. Hence, T-independent antigens do not produce long-lasting immune responses.  

Similarities Between T-Cell Dependent and Independent Antigens

• T-dependent and independent antigens are two types of antigens that elicit immune responses.
• Also, both types of antigens undergo B cell activation.

Difference Between T Dependent and Independent Antigens

Definition

T-dependent antigens refer to an immunogen that requires T cell cooperation with B cells to synthesize specific antibodies. In contrast, T-independent antigens refer to typic polysaccharides that can induce B-cell proliferation and antibody secretion in the absence of T cells.

Help of T Cells

T-dependent antigens require the help of T cells to activate B cells, while T-independent antigens do not require the help of T cells to activate B cells.

Types

Most protein antigens are T-dependent, while polymeric molecules with repeated antigenic determinants, such as polysaccharides, are T-independent antigens.

Valency of Antigen

While T-dependent antigens are monovalent, T-independent antigens are multivalent.

Time Period

T-dependent antigens are fast and require 1-2 days, while T-independent antigens are slower and take several days to initiate a response.

Types of Antibodies

T-dependent antigens react predominantly with IgM, but T-independent antigens react with all Ig isotypes.

Long Lasting Serum Antibody Titers

T cell-dependent antigens produce long-lasting serum antibody titers, while T cell-independent antigens do not produce long-lasting antibody titers.

Conclusion

In brief, T cell-dependent and T cell-independent antigens are two types of antigens that undergo B cell activation. T cell-dependent antigens require the help of T cells to activate B cells. Most T-dependent antigens are proteins, and they are monovalent. Moreover, these antigens quickly initiate immune responses and predominantly react with IgM antibodies. However, T-dependent antigens produce long-lasting serum antibody titers.

In comparison, T cell-independent antigens do not require the help of T cells for the activation of B cells. They are multivalent antigens that slowly initiate immune responses. They react with all types of antibody isotypes. But T-independent antigens do not produce long-lasting immune responses. Therefore, the main difference between T-dependent and T-independent antigens is their requirement for T cells to activate B cells.

References:

1. Thymus dependent antigen. ScienceDirect Topics. 

Image Courtesy:

1. “Activation of T and B cells” By Immcarle105 – Own work (CC-BY SA4.0) via Commons Wikimedia
2. “T independent B cell Activation” By סתו כסלו – Own Work (CC-BY SA 4.0) via Commons Wikimedia