Immune response to intramuscular injection of the circulating antigen (literature review)
When an intramuscular injection of a circulating antigen, taken from venous blood, is administered, the immune response involves both the innate and adaptive immune systems. Here’s how each system responds:
Innate Immune Response
1. Local Inflammation: The injection site experiences an immediate local inflammatory response. This involves the recruitment of innate immune cells such as neutrophils, monocytes, and dendritic cells to the site of injection to initiate recognition and processing of the antigen.
2. Antigen Uptake and Presentation: Innate immune cells, particularly DCs, capture the antigen. These antigen-presenting cells (APCs) process the antigen and migrate to the draining lymph nodes. Here, they present the antigen (in the form of MHC-II with epitope ) to T cells, bridging the innate and adaptive immune responses.
3. Cytokine Production: The interaction with the antigen leads to the production of pro-inflammatory cytokines and chemokines, which further recruit immune cells to the site and enhance the inflammatory response.
Adaptive Immune Response
1. Activation of T Cells: Once in the lymph nodes, APCs present the processed antigens to CD4+ helper T cells via major histocompatibility complex (MHC) class II molecules. This activation is crucial for initiating a specific adaptive immune response.
2. B Cell Activation and Antibody Production: Helper T cells assist in activating B cells that recognize the same antigen. This leads to their differentiation into plasma cells that produce specific antibodies against the antigen.
3. Memory Formation: Some activated T and B cells become memory cells, providing long-term immunity by enabling a faster response upon future exposures to the same antigen.
Response to Antigen/Antibody Complexes
• Complex Formation: If antibodies are already present in circulation, they may bind to the injected antigens forming antigen-antibody complexes.
• Enhanced Phagocytosis: These complexes can enhance phagocytosis by binding to Fc receptors on phagocytes, leading to more efficient clearance of antigens.
• Complement Activation: The complexes can also activate the complement system, further promoting inflammation and opsonization.
Overall, while both innate and adaptive responses are activated by intramuscular injections of circulating antigens, the innate response provides immediate defense and sets up conditions for a more targeted adaptive response. The presence of pre-existing antibodies can modify this response by forming complexes that enhance certain immune pathways.