The immune system's two-pronged approach combines innate and adaptive responses to protect us from harm. Innate immunity acts fast, using physical barriers and non-specific cells to fend off invaders. It's our body's first line of defense, always ready to fight.
Adaptive immunity takes longer but packs a punch. It uses specialized cells to target specific threats and remembers them for future battles. This dynamic duo works together, keeping us safe from countless pathogens we encounter daily.
Innate Immune System
First Line of Defense: Physical and Chemical Barriers
- Physical barriers act as the first line of defense against pathogens and include the skin, mucous membranes, and cilia
- Skin provides a physical barrier that is difficult for pathogens to penetrate and also secretes antimicrobial substances (sebum, lysozyme)
- Mucous membranes line the respiratory, digestive, and urogenital tracts and secrete mucus that traps pathogens
- Cilia in the respiratory tract sweep trapped particles and mucus upward to be expelled or swallowed
Cellular Components of Innate Immunity
- Phagocytes, such as neutrophils and macrophages, engulf and destroy pathogens through a process called phagocytosis
- Natural killer cells (NK cells) recognize and kill virus-infected cells and tumor cells by releasing cytotoxic granules
- Phagocytes and NK cells release cytokines that attract other immune cells to the site of infection and promote inflammation
Humoral Components of Innate Immunity
- Complement system consists of a series of proteins that enhance the immune response by promoting inflammation, opsonization, and lysis of pathogens
- Complement proteins can directly lyse bacteria by forming membrane attack complexes (MAC) on their surface
- Inflammation is a localized response to tissue damage or infection that involves increased blood flow, capillary permeability, and immune cell infiltration
- Inflammatory response is characterized by redness, swelling, heat, pain, and loss of function in the affected area
Adaptive Immune System
Lymphocytes: Key Players in Adaptive Immunity
- Adaptive immunity is mediated by lymphocytes, which include B cells and T cells
- B cells mature in the bone marrow and are responsible for antibody production (humoral immunity)
- T cells mature in the thymus and are involved in cell-mediated immunity, including helper T cells (CD4+) and cytotoxic T cells (CD8+)
- Helper T cells activate B cells and other immune cells, while cytotoxic T cells directly kill infected or cancerous cells
Specificity and Memory in Adaptive Immunity
- Adaptive immunity is highly specific, with each lymphocyte recognizing a unique antigen through its antigen-specific receptor (B cell receptor or T cell receptor)
- Antigen presentation by antigen-presenting cells (APCs) is crucial for the activation of T cells and the initiation of the adaptive immune response
- Adaptive immunity develops memory, allowing for a faster and stronger response upon subsequent exposure to the same antigen
- Memory B cells and memory T cells persist after an infection is cleared, providing long-lasting protection against future infections by the same pathogen