What is Cell-Mediated Immunity?
Cell-mediated immunity (CMI) is a crucial aspect of the adaptive immune system that involves the activation of
T cells to defend against pathogens. Unlike
humoral immunity, which relies on antibodies to combat foreign invaders, CMI primarily targets infected cells, cancer cells, and foreign tissues. This type of immunity is essential for combatting intracellular pathogens like viruses, certain bacteria, and fungi.
How Does Cell-Mediated Immunity Work?
CMI involves several steps. The process begins with the presentation of antigens by
antigen-presenting cells (APCs), such as
macrophages and
dendritic cells. These cells engulf pathogens and present their antigens on their surface via major histocompatibility complex (MHC) molecules.
Helper T cells (CD4+ T cells) recognize the antigens presented by MHC class II molecules and become activated. Subsequently, they release cytokines that stimulate other immune cells.
What Role Do Cytotoxic T Cells Play?
Cytotoxic T cells (CD8+ T cells) are pivotal in CMI. They identify infected cells by recognizing antigens presented by MHC class I molecules. Once activated, these cells directly kill infected cells by inducing apoptosis, ensuring the pathogen is eradicated. This is particularly important in viral infections where pathogens reside inside host cells, shielded from antibodies.
How is CMI Involved in Infectious Diseases?
In infectious diseases, CMI is critical for the defense against pathogens that have evolved to evade humoral immunity. For example, in
tuberculosis, caused by Mycobacterium tuberculosis, the bacteria can survive inside macrophages. CMI is essential for activating these macrophages to kill the bacteria. Similarly, in viral infections like
HIV/AIDS, CMI is crucial as it targets virus-infected cells, although the virus itself attacks CD4+ T cells, weakening the immune response.
What Are the Challenges in CMI?
Several challenges affect the efficacy of CMI. Pathogens have developed strategies to evade CMI by inhibiting antigen presentation or inducing the death of T cells. Additionally, some pathogens cause chronic infections due to an inadequate CMI response. In conditions like
autoimmune diseases, dysregulated CMI can lead to tissue damage as the immune system attacks the body’s own cells.
How Can CMI Be Enhanced?
Enhancing CMI is a significant focus in vaccine development and
immunotherapy. Vaccines aim to induce robust CMI by mimicking natural infection, leading to the activation of T cells. In cancer immunotherapy, strategies like
CAR T-cell therapy involve engineering T cells to better recognize and attack cancer cells. Additionally, researchers are exploring ways to boost CMI through adjuvants that enhance the immune response and by developing novel therapeutics that target immune checkpoints.
Conclusion
Cell-mediated immunity is a vital component of the immune system, providing protection against a range of infectious diseases. Understanding its mechanisms and challenges allows for the development of targeted therapies and vaccines. As research progresses, enhancing CMI holds promise for improved management of infectious and autoimmune diseases, as well as cancer.
