Adaptive immune system

SEM Lymphocyte

Ngram acquired immunity vs. adaptive immunity

Primary immune response 1

Antigen presentation

T cell activation

Adaptive immune system

The adaptive immune system, also known as the acquired immune system or, more rarely, as the specific immune system, is a subsystem of the overall immune system that is composed of highly specialized, systemic cells and processes that eliminate or prevent pathogen growth. In contrast to the innate immune system, which is a first-line defense and responds more generally to pathogens, the adaptive immune system is highly specific to each pathogen it encounters. It is characterized by its ability to learn from encounters with pathogens and to improve its responses to these pathogens over time.

Overview

The adaptive immune system is activated by the exposure to pathogens. Once activated, it creates an army of immunological memory cells that remember the specific pathogen encountered. This memory allows the adaptive immune system to mount a faster and more efficient response upon subsequent exposures to the same pathogen. The main components of the adaptive immune system include T lymphocytes (T cells), B lymphocytes (B cells), and antibodies.

Components

T Lymphocytes

T cells are a type of white blood cell that play a critical role in the immune response. There are several types of T cells, each with a specific function. Helper T cells assist in the activation of B cells and other T cells. Cytotoxic T cells are responsible for attacking and killing infected cells. Regulatory T cells help to control the immune response, preventing autoimmune diseases.

B Lymphocytes

B cells are another type of white blood cell. They are primarily involved in producing antibodies against antigens, which are substances that the immune system recognizes as foreign. Each B cell is programmed to make one specific antibody. When a B cell encounters its triggering antigen, it begins to divide rapidly and produce large quantities of its antibody.

Antibodies

Antibodies, also known as immunoglobulins, are Y-shaped proteins that are produced by B cells. They bind to specific antigens, marking them for destruction by other immune cells. Antibodies can neutralize pathogens directly, agglutinate pathogens, or opsonize pathogens, enhancing their uptake and destruction by phagocytes.

Function

The adaptive immune system functions through two main mechanisms: humoral immunity and cell-mediated immunity. Humoral immunity involves the production of antibodies by B cells. Cell-mediated immunity does not involve antibodies but instead relies on the activation of T cells to eliminate infected cells.

Humoral Immunity

In humoral immunity, B cells produce antibodies after being activated by helper T cells. These antibodies circulate in the bloodstream and lymphatic system, binding to antigens and neutralizing pathogens or marking them for destruction.

Cell-Mediated Immunity

Cell-mediated immunity involves the direct action of T cells. Cytotoxic T cells recognize and kill infected cells. Helper T cells play a role in activating both B cells and cytotoxic T cells, while regulatory T cells help to dampen the immune response once the infection has been cleared to prevent excessive damage to the host.

Memory

One of the hallmark features of the adaptive immune system is its ability to remember past infections. Memory T cells and memory B cells are long-lived cells that remain in the body after an infection has been cleared. These cells can mount a rapid and robust response to subsequent infections by the same pathogen, often preventing the pathogen from causing disease.

Conclusion

The adaptive immune system is a critical component of the body's defense against pathogens. Its ability to remember past encounters and improve its response to infections makes it essential for long-term immunity. Understanding the mechanisms of the adaptive immune system is crucial for the development of vaccines and therapeutic interventions for infectious diseases.