Innate Immunity Overview

Study Notes

Innate Immunity

Cause: Exposure to pathogens, injury, or cellular damage triggers the innate immune system. Common triggers include microbial antigens and damage-associated molecular patterns (DAMPs).
Pathophysiology:
- Recognition of Threats: Pattern recognition receptors (PRRs) recognize pathogen-associated molecular patterns (PAMPs) on microbes.
- Inflammatory Cells: Inflammatory cells (mast cells, macrophages, dendritic cells) become activated.
- Cytokine and Chemokine Release: Activated cells release cytokines (TNF-α, IL-1, IL-6) and chemokines, recruiting other immune cells to the infection site. Mast cells release histamine, leading to vasodilation and increased vascular permeability.
- Immune Cell Recruitment: Neutrophils and macrophages are recruited to engulf pathogens via phagocytosis. Natural killer (NK) cells destroy virus-infected cells and tumor cells.
- Systemic Manifestations: Cytokine release causes fever and triggers the acute-phase response (increased CRP and fibrinogen production). This response aids in containing and eliminating infections, and promotes tissue repair.
Transmission: Not transmissible. Innate immunity is a natural defense mechanism present at birth.
Risk Factors: Age (newborns and elderly), chronic illnesses (diabetes, cardiovascular disease, cancer), immunosuppression (chemotherapy or immunosuppressive medications), lifestyle factors (smoking, poor diet, inactivity), and genetic disorders (primary immunodeficiencies like SCID).

Adaptive Immunity

Cause: Exposure to specific antigens (viral, bacterial, or parasitic) through infection or vaccination.
Pathophysiology:
- Antigen Recognition: Antigen-presenting cells (APCs) like dendritic cells and macrophages present antigens to T-helper (Th) cells via MHC class II molecules.
- Antibody Production: B cells differentiate into plasma cells releasing antibodies. Memory B cells remain for future responses.
- Cell-Mediated Immunity: Cytotoxic T cells (CD8+ T cells) kill virus-infected cells. Memory T cells enable a quicker response.
Transmission: Not transmissible. Adaptive immunity is not inheritable.
Risk Factors:
- Chronic Illnesses: Conditions like diabetes, cardiovascular disease, and cancer can reduce innate immune response efficiency.
- Immunosuppression: Chemotherapy or immunosuppressive medications weaken the innate immune response.
- Lifestyle Factors: Smoking, poor diet, and inactivity are linked to chronic inflammation, which can dysregulate innate immunity.
- Age: Elderly individuals experience reduced T cell and B cell function.
- HIV/AIDS: Targets CD4+ T cells, impairing adaptive immunity.
- Autoimmune Disorders: Can cause the immune system to attack itself.
- Vaccination Status: Lack of vaccination may result in a lack of immune memory.
- Immunosuppressive Therapy: Chemotherapy or corticosteroids can impair adaptive immunity.
- Genetic Disorders: Primary immunodeficiencies like SCID impair B and T cells function.
- Chronic Illnesses: Chronic illnesses (diabetes, cardiovascular disease and cancer) reduce innate immune response efficiency.
- Immunosuppression: Chemotherapy or immunosuppressive medications weaken the innate immune response.
- Lifestyle Factors: Smoking, poor diet, and inactivity are linked to chronic inflammation, dysregulating innate immunity.
- Age (elderly): In elderly, innate immune response is reduced due to reduced T-cell and B-cell function.
- HIV/AIDS: Impacts CD4+ T cells which affects adaptive immunity.
- Autoimmune disorders: Immune system attacks healthy tissues.
- Vaccination Status: Lack of vaccination leads to lack of immune memory for specific pathogens.
- Immunosuppressive Therapy: Chemotherapy/corticosteroids impair adaptive immunity.
- Genetic Disorders: Primary immunodeficiencies such as SCID impair B and T cells.