Immunology Flashcards
Explain roughly how the immune system is organised
The immune system is composed of two main arms:
- the innate (nonspecific) immune response
- the adaptive or acquired (specific) immune response
Describe the different constituants of the innate immune response
The innate response is composed of:
- anatomic and physiologic barriers (i.e., skin, mucous membranes, temperature, pH and oxygen levels)
- chemical compounds including digestive enzymes, antimicrobial peptides and cytokines - cellular components (i.e., phagocytic and cytotoxic cells, complement, kinins, leukotriens, prostaglandins, neutrophils, eosinophils, basophils, mast cells and natural killer lymphocytes)
What is the role of NK lymphocytes
NK lymphocytes are important mediators of cell-mediated immunity
What is the role of monocytes/macrophages
Monocytes = phagocytic cells circulating in the blood
Macrophages = these cells in tissue
What is the role of dendritic cells
Dendritic cells are distinct phagocytic cells found in tissue and lymphoid cells
They provide important signals for the T lymphocytes
Explain how does the innate immune response work
The innate immune response is not specific in terms of antigen recognition
Microbial agents contain unique molecules not found in higher organisms, referred to as pathogen-associated molecular patterns (PAMPs)
The phagocytic cells (i.e., macrophages, dendritic cells and neutrophils) express a variety of receptors that recognize PAMPs, allowing recognition of pathogens, and enhancing phagocytosis and destruction of the pathogen by these cells
Neutrophils are often the first cells on the scene and migrate from the blood vessels to the affected tissue
Granulocytic cells will secrete important inflammatory mediators (e.g., histamine, proostaglandin) and cytokines and chemokines that mediate intercellular communication
- an important group of cytokines that function in innate immunity is the interferon family
- interferons mediate a variety of biologic functions and function as immunomodulators, as well as an inducer of antiviral state in cells
Describe the different constituants of the acquired immune response
The acquired immune response is comprised of a variety of lymphocytes:
- B lymphocytes: antibody factories of the immune system (secretors are termed plasma cells), and also function as antigen-presenting cells for the T helper lymphocytes
- T lymphocytes:
- T regulatory lymphocytes
- cytotoxic T lymphocytes: specifically target cells that have been altered and induce apoptosis in the target cell
What is the fundamental difference between the acquired and the innate immune responses
The adaptive (=acquired) immune response exists to specifically recognize and eliminate a pathogen
- lymphocytes recognize small slight differences and exhibit immunologic memory
Unlike the innate response, the adptive response takes time to develop, but it also improves as it develops
How do B lymphocytes work
B lymphocytes develop in the bone marrow, and express immunoglobulins on their surface that function in antigen recognition and binding
- B lymphocytes bind free antigen
After antigen encounter, the B lymphocyte proliferates and differentiates into plasma cells or memory cells
How do T lymphocytes work
T lymphocytes leave the bone marrow and mature in the thymus
The antigen-binding receptor of T lymphocytes is referred to as the T cell receptor
- unlike B lymphocytes, the T cell receptor recognizes antigen only when it is bound to self major histocompatibility complex molecules
T lymphocytes are divided into 2 lineages based on differing functions and cell surface markers
- cytotoxic T lymphocytes expressing CD8 cell marker recognize antigen displayed on MHC I (expressed on all cells), and function to induce apoptosis in the cell displaying nonself or foreign antigen
- T helper lymphocytes function in modulation of the immune response via cytokines and cell surface molecule expression
- TH1 promotes a cell mediated response
- TH2 promotes a humoral response
In the adaptive immune response, the lymphocyte must encounter the antigen for which it is specific
Explain the difference between the humoral and the cell-mediated responses
The humoral response, constituted by antibodies, mediates protection against extracellular pathogens
The cell-mediated response fights intracellular pathogens by eliminating the cell that harbors them
The T helper lymphocytes are critical to humoral and cell mediated functions
Describe how the antigen-specific response follows the innate response
Following phagocytosis and microbial destruction, free antigen (i.e., breakdown products, organisms) and activated antigen presenting cells migrate to regional lymph nodes
Interaction with B and T lymphocytes
Lymphocytes activation, proliferation and differentiation into effector and memory cells
- lymphocyte effectors migrate to the site of inflammation
- memory lymphocytes will recirculate to the site of initial antigen encounter and activation
Effector cells eliminate pathogen and memory cells persist to provide protection against future infections with the same pathogen
