Immune response to intracellular parasites:
Cellular immunity
Intracellular parasites are pathogens that have the ability to infect and replicate within host cells. Examples of intracellular parasites include viruses, bacteria (e.g., mycobacteria, chlamydiae), parasites (e.g., Plasmodium, Toxoplasma), and fungi (e.g., Histoplasma).
The immune response to intracellular parasites involves a coordinated effort between innate and adaptive immune mechanisms. Innate immune cells, such as macrophages and dendritic cells, recognize and engulf intracellular parasites through pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs) and NOD-like receptors (NLRs). Once engulfed, these cells can either destroy the pathogen through phagocytosis and lysosomal degradation, or present antigens on their surface to activate adaptive immunity.
Adaptive immunity to intracellular parasites is primarily mediated by CD4+ T-helper cells and CD8+ cytotoxic T lymphocytes (CTLs). CD4+ T-helper cells recognize antigens presented by dendritic cells and macrophages, after which they differentiate into various subsets that coordinate different aspects of the immune response. For example, Th1 cells produce interferon-gamma (IFN-γ), which activates macrophages to enhance their antimicrobial activity. Th2 cells produce cytokines that stimulate B cell proliferation and antibody production. Th17 cells promote recruitment of neutrophils to the site of infection to control extracellular pathogens.
CD8+ CTLs recognize and kill infected host cells presenting intracellular parasite antigens on their surface. These CTLs are crucial for controlling intracellular infections where the pathogen can hide from immune surveillance within host cells. CTLs recognize their targets through the presentation of peptide antigens on major histocompatibility complex (MHC) class I molecules on the surface of infected cells.
In summary, the immune response to intracellular parasites involves a combined effort of innate and adaptive immunity, with innate cells recognizing and phagocytosing intracellular parasites, and adaptive cells generating specific immune responses, including cytokine production, B cell activation and antibody production and CTLs activation and killing of infected cells.
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