CD4, CD40L, CXCR4/CCR5.
Natural Killer cells kill pathogens extracellularly.
Mesenteric lymph nodes are located in the mesentery, associated with the intestines.
CD8 serves as a co-receptor for MHC-I.
Macrophages are also known as 'large-eater' or histiocyte.
M1 macrophages secrete pro-inflammatory cytokines such as IL-1, IL-6, IL-8, and TNF-α.
Dendritic cells function as a 'bridge' between innate and adaptive immune responses.
Fever is a host defense mechanism against infectious diseases, particularly bacterial infections.
Immunological memory allows antigen-specific B cells (and T cells) to respond more quickly and robustly to antigen on repeated encounters, known as an anamnestic reaction.
Antibodies neutralize pathogens and toxins and assist with the activation of the complement system.
Hematopoietic stem cells (HSC), which are multipotent and give rise to RBCs, WBCs, and platelets.
Antibodies recognize and bind (opsonize) the antigens that caused their production, assisting with phagocytosis.
Neutrophilia is the increased number of neutrophils, typically occurring during infections with bacteria and fungi due to increased granulopoiesis.
Pathogens enter the body’s soft tissues, stimulating the innate immune responses to destroy the invading pathogens.
Recurrent life-threatening infections, neurological defects, oculocutaneous albinism, and neutrophils with excessive nuclear segmentation and giant lysosomes.
LYST is critically involved in lysosomal transport and vesicle formation during phagocytosis.
The red pulp removes spent RBCs, recycles iron, stores platelets, and stores blood that can be mobilized in the event of hemorrhagic shock.
Cervical, Supraclavicular, Axillary, Popliteal, Femoral, Inguinal, Mesenteric, Supratrochlear, Mediastinal.
Cells inside lymph nodes respond to antigens present in interstitial fluid (ISF) drained from upstream tissues.
Intracellular, oxidative and non-oxidative mechanisms.
In adults, red bone marrow is found in the vertebrae, epiphyses of long bones, innominate bones of the pelvis, and flat bones of the skull, sternum, and ribs.
Memory T cells keep immunological memory of the antigen and differentiate into effector T cells upon re-encountering the antigen, also helping with activation of B cells during re-infection.
Fluid from the blood seeps out of capillaries into the tissues, creating interstitial fluid.
GALT refers to organized lymphoid tissue and single lymphoid follicles present across the gut wall.
B and T cells get activated in the MALT and then traffic to the draining mesenteric lymph node to amplify the adaptive immune response.
The Complement System is one of the key responses that aids in the immune defense, details will be covered in DSA-2 and TBL-5.
The thymus is composed of many lobules defined by a capsule and trabeculae, with each lobule containing a dense outer cortex and a less dense inner medulla.
Red bone marrow is the site of hematopoiesis and B cell lymphopoiesis, producing blood elements and lymphocytes.
Antibodies are found in blood serum, tissue fluids, and mucosal surfaces.
Eosinophilia, especially in allergic responses and infections with helminthic parasites.
They recognize and help destroy any pathogen that crosses the barriers.
Lactobacillus spp. and Candida albicans are examples of normal flora found in the vaginal cavity.
1) Complement System 2) Acute Inflammatory response 3) Phagocytosis 4) Fever
Lymph nodes, spleen, and mucosal-associated lymphoid tissues (MALTs).
C3a and C5a.
Lymphatic fluid is extracellular fluid found inside lymphatic vessels and lymph nodes, formed by the drainage of excess interstitial fluid (ISF).
~60%
Monocytes secrete pro-inflammatory cytokines when stimulated.
1-4%
CD stands for cluster of differentiation.
Immune cells produce cytokines and chemokines that function as signaling molecules.
CD16 binds the Fc of IgG.
T lymphocytes (T cells), B lymphocytes (B cells), and Natural Killer (NK) cells.
The lymphatic system supports the circulation of lymph and immune cells (B cells, T cells, DCs) to secondary immune organs, facilitating adaptive immune function.
Cytotoxic T cells kill host cells infected with viruses or intracellular bacteria, as well as cancer/tumor cells, targeting intracellular antigens.
T helper (Th) cells and Cytotoxic T (Tc) cells (or Cytotoxic T lymphocytes).
Antigens are pumped through lymphatic vessels into draining lymph nodes, where they activate adaptive immune cells.
Activated B and T cells migrate through lymphatic vessels into systemic circulation and then relocate to affected mucosa.
It is one of the key responses of the Innate Immune System, with more details to be discussed in TBL-5.
Memory B cells keep immunological memory of the antigen and differentiate into effector B cells upon re-encountering the antigen.
The spleen is serviced by blood vessels but does not have afferent lymphatic vessels, meaning it does not drain lymphatic fluid.
Polymorphonuclear Neutrophilic Leukocytes (PMNs)
They die and form pus.
Monocytes, Macrophages, Lymphocytes, Dendritic cells
Monocyte-like in appearance, may have dendritic processes
They work side by side through a feedback mechanism.
The secondary immune response indicates an elevated antibody response due to immunological memory.
Production of antibodies, Keeping immunological memory
Physical barriers, chemical and physiological barriers, and normal microbiota that block infection.
B cell receptors (BCRs) and T cell receptors (TCRs).
Natural Killer Cells use direct cytotoxicity via perforin-granzyme and antibody-dependent cell-mediated cytotoxicity (ADCC) using Fc Ƴ III receptors.
Developmental origin, cytological appearance, location, and immune functions.
They work in a cascade to stimulate the inflammatory response, opsonize pathogens for phagocytosis, and form the membrane attack complex for cytolysis.
Blood consists of plasma, platelets, and cells including red blood cells (RBC) and white blood cells (WBC).
Monocytes are phagocytic cells that participate in the elimination of bacteria and fungi, secrete pro-inflammatory cytokines, and can present antigens.
Monocytes contribute to cytotoxic killing through degranulation and antibody-dependent cellular cytotoxicity (ADCC).
Bi-lobed or polymorphonuclear (multi-lobed appearance)
Macrophages are the first cells to encounter antigens that have entered the skin, lymph node, spleen, or liver.
Phagocytosis is the opsonization-mediated uptake of pathogens by phagocytic cells, leading to their intracellular destruction via oxidative and non-oxidative killing mechanisms.
The temperature-regulation center in the brain raises the normal temperature of 37°C in response to pyrogens produced by infecting microbes and by macrophages and monocytes.
Secretion of cytokines, Elimination of cancer cells and virally infected host cells
Normal flora can be found on the skin, eyes, GI tract, outer ear, nose, mouth, throat, urethra, and vagina.
Neutropenia is a decreased number of neutrophils, which can occur in cancer patients treated with antiproliferative agents, leading to increased susceptibility to bacterial and fungal infections.
Tissue resident leukocytes that are not found in the blood.
The thymus produces thymosin and thymic stromal lymphopoietin.
The two distinct regions of the spleen are the red pulp and the white pulp.
Interstitial fluid surrounds cells in the tissues (interstitium) and facilitates the transfer of nutrients and wastes to/from cells and capillaries.
The skin surface pH ranges from 5.0 to 5.5.
Serotonin, histamine, bradykinin, prostaglandins, leukotrienes, and thromboxane are examples of inflammatory mediators.
Monocytes are phagocytic and play a role in the elimination of bacteria and fungi; they can also present antigens.
The two classes are M1 macrophages, which secrete pro-inflammatory cytokines, and M2 macrophages, which secrete anti-inflammatory cytokines.
They are involved in allergic disorders and the inflammatory response to parasitic infections.
CD34 is involved in cell-cell adhesion.
APCs, such as dendritic cells and macrophages, present epitopes on their cell surface after phagocytosis and connect innate immunity with adaptive immunity by activating and proliferating naïve T lymphocytes.
It enables the elimination of pathogens before the host can become symptomatic, thus providing the host with immunity.
Eosinophils preferentially reside in the dermis and lamina propria.
In the bone marrow.
Leukocytes
Neutropenia can be treated with rhG-CSF (recombinant human granulocyte colony-stimulating factor) to stimulate granulopoiesis.
ADCC involves NK cells binding to antibody-coated antigens on infected or cancer cells via Fc Ƴ III receptors, leading to the release of granzyme and perforin to induce apoptosis.
Plasma B cells secrete antibodies specific to the antigens.
The spleen participates in immune responses against antigens in the blood introduced via trauma, insect bites, or disseminated infection.
Lymph nodes consist mostly of B and T cells, some macrophages, and dendritic cells (DCs).
They are the first to respond and are a hallmark of acute inflammation.
Polymorphonuclear with pink cytoplasmic granules
Cell surface markers are various surface glycoproteins that immune cells rely on to communicate and interact.
Opsonization is the process of coating antigens with host proteins (opsonins) that enhance phagocytosis by binding to epitope-specific receptors.
Skin acts as an outer barrier composed of densely packed squamous epithelial cells and impenetrable keratinized cells.
They produce large amounts of type-I interferons (IFN-alpha, IFN-beta) but do not function as APCs.
The lymphatic system drains and cleans excess interstitial fluid (ISF) to help maintain fluid balance and returns approximately 8 liters per day into the cardiovascular system.
Blood, Lymph, LNs
Memory B cells and Plasma B cells.
Adaptive immune cells (B and T cells) and their products that help defend the host and maintain memory of the pathogen.
Severe Congenital Neutropenia is a genetic disorder affecting granulopoiesis, manifesting in early infancy with life-threatening bacterial infections, particularly from Staphylococcus spp.
Perforin forms a pore on the infected or neoplastic cell, allowing granzyme to enter and induce apoptosis.
Spontaneous organized lymphoid structures that arise in chronic inflammation, select cancers, and in select autoimmune diseases.
Cytolysis is the process where the membrane attack complex formed by C5b, C6-C9 causes lysis and death of target cells.
Lymph nodes are small (1-2 cm in size, <1 gm), bean-shaped organs.
Lymph nodes are major sites for B and T cell activation and for mounting adaptive immune responses.
Eosinophils are located in blood and tissue, and their role is cytotoxic, particularly in the elimination of extracellular parasites and in allergic responses.
Mast Cells are involved in degranulation and play a role in acute inflammation and allergic responses through the release of inflammatory mediators.
M2 macrophages have roles in wound healing and tissue repair by secreting anti-inflammatory cytokines like IL-10 and TGF-β.
Dendritic cells and macrophages act as Antigen-Presenting Cells (APCs) that process and present antigens to T cells.
BALT stands for bronchus-associated lymphoid tissue, which is located in the bronchial region.
Granulocytes (neutrophil, eosinophil, basophil), Monocyte, Macrophage (M Φ), Dendritic cell (DC), Mast cell, Megakaryocyte (platelet precursor), Erythrocyte (RBC).
In adults, red bone marrow is located in specific bones, while in infants, it has a distinct distribution pattern.
Blood, Lymph, LNs
ADCC mechanism involves binding targets using the high affinity receptor FcɛRI and antibodies IgE or IgG, then killing targets by releasing cytotoxic proteins and cytokines.
MALTs are lymphoid aggregates present in the lamina propria of mucosal membranes lining the GI, respiratory, and urogenital tracts.
A condition caused by defects in lysosomal trafficking regulator (LYST), leading to impaired phagocyte function and recurrent infections.
Infections caused by fungi, Gram-negative bacteria, and Gram-positive bacteria such as Staphylococcus and Streptococcus spp.
A system comprising a group of interacting proteins produced by the liver and circulating in the blood, which are inactive when intact and active when fragmented.
Humoral immunity typically targets and destroys extracellular pathogens.
Lactobacilli produce lactic acid, maintaining a vaginal pH of 3.8-4.5.
Acute phase proteins and cytokines are involved in the innate immune response.
NK cells are cytotoxic and are responsible for the elimination of tumor/cancer cells and virally infected host cells.
Normal variants of macrophages include Kupffer cells (in liver), alveolar macrophages (in lungs), Langerhans cells (in skin), microglia (in brain), and osteoclasts (in bone).
PRRs are non-specific receptors on immune cell surfaces that recognize and bind to Pathogen-Associated Molecular Patterns (PAMPs) found on pathogens.
Mechanical removal processes include peristalsis, flushing of the urinary tract, and mucociliary clearance of the respiratory tract.
Conventional or myeloid DCs (cCDs or mDCs) and plasmacytoid dendritic cells (pDCs).
The acute inflammatory response is triggered by foreign bacteria entering tissues or tissue damage.
Fluid uptake allows for antigens present in tissues to be delivered to secondary immune organs, aiding in the activation of T and B cells and the initiation of immune responses.
Lymphatic vessels collect excess interstitial fluid from tissues and return it as lymphatic fluid to the blood vasculature.
Smooth muscles, respiratory pump, and skeletal muscle pump help suck excess interstitial fluid into lymphatic capillaries.
Microfold cells transport antigens in Peyer's patches and play a central role in mounting adaptive immune responses at mucosal sites.
Red bone marrow and thymus.
Phagocytosis is one of the key responses of the Innate Immune System, involving the engulfing of pathogens by immune cells.
Antibodies are Y-shaped glycoproteins produced by activated B cells (plasma cells) in response to specific antigens.
Lymphatic fluid is returned to the cardiovascular system via subclavian veins where it mixes with venous blood.
Defensins are antimicrobial peptides produced by all epithelia that kill bacteria, fungi, and enveloped viruses by disrupting their membranes.
Pus.
Dendritic Cells are phagocytic and are the main cells to present antigens to T cells, helping to mount the adaptive immune response.
Macrophages perform phagocytic killing, antigen processing and presentation, and are major producers of cytokines when stimulated.
The physical defenses include skin, which is made of densely packed squamous epithelial cells and keratinized cells, and mucosal epithelia that line the digestive, respiratory, and urogenital tracts, secreting mucus and protective enzymes.
Macrophages phagocytose pathogens and kill them intracellularly, while Natural Killer cells kill pathogens extracellularly.
Colonic lymphoid nodules are aggregates of immune cells found in the colon, contributing to gut immunity.
The cardinal signs of acute inflammation are redness, warmth, pain, swelling, and altered function.
ADCC is a mechanism by which antibodies assist in killing infected cells of the host.
B cells and T cells.
Examples of normal flora on the skin include Propionibacterium and Staphylococcus epidermidis.
Natural Killer Cells are lymphocytes that function in innate immunity by eliminating virally-infected and neoplastic (cancer/tumor) cells.
By squeezing out through blood vessel walls upon receiving a chemical signal (Chemotaxis).
Fever is a key response that helps to enhance the immune response and inhibit pathogen growth.
The antigen-specific B cell receptor (BCR) can be secreted as an antibody (Ab) or immunoglobulin (Ig).
Dendritic cells (DCs), B cells, and T cells are carried in lymph through the lymphatic vessels.
Lysozyme, Lactoferrin, and Peroxidase are antimicrobial enzymes present in tears, phagocytes, saliva, and other secretions.
Phagocytic and cytotoxic; they are the key first responders to infection and play a role in the elimination of bacteria and fungi.
Macrophages are phagocytic and play a role in acute/chronic inflammation through the release of inflammatory mediators; they can also present antigens.
Neutrophils, Eosinophils, and Basophils.
Mucosal epithelium secretes mucus composed of glycoproteins, proteoglycans, and protective enzymes, aiding in the mechanical removal of microbes.
NALT stands for nasopharyngeal-associated lymphoid tissue, which is involved in immune responses in the nasopharyngeal region.
Urogenital-associated lymphoid tissue is involved in immune responses in the urogenital tract.
T helper cells secrete cytokines that shape immune responses by enhancing or suppressing immune cell functions, acting as the 'central gate keepers'.
Normal flora refers to the microorganisms that are naturally present in various parts of the body, such as the skin, eyes, GI tract, and more.
Examples of normal flora in the large intestine include Escherichia coli and Clostridium difficile.
Failure of either the innate or adaptive immune division, especially if there is a failure in innate immunity.
They are sites where naïve adaptive immune cells interact with antigens, get activated, and mount a response to foreign antigens.
They are less organized compared to secondary immune organs.
The 5 major structural classes or isotypes of antibodies are IgA, IgD, IgE, IgG, and IgM.
Draining lymph nodes filter lymphatic fluid (lymph) transported via lymphatic vessels.
Once in tissue, monocytes differentiate into macrophages or dendritic cells (DCs).
Basophils are involved in degranulation, releasing inflammatory mediators such as histamine, and play a role in allergic responses.
Resident macrophages typically reside in tissues and secondary immune organs.
Neutrophils are the first to respond to infection, chemotaxing to the infection site within minutes to hours.
It induces cross-linking of multiple Fc ε Rs, which can lead to acute allergic reactions.
GALT refers to gut-associated lymphoid tissue, which includes structures like Peyer's patches and mesenteric lymph nodes.
Cytotoxic killing (degranulation, ADCC) and elimination of extracellular parasites, especially helminths, by ADCC.
In the thymus.
To recognize and destroy invading antigens and neoplastic cells, and alert other cells of the immune system.
The thymus is the site of thymopoiesis, the process of development of T cells.
The thymus consists of progenitor T cells (thymocytes), stromal cells, thymic epithelial cells, macrophages, and dendritic cells.
C3b opsonizes pathogens, thereby helping with phagocytosis.
500-800 lymph nodes.
Monocytes are found in low numbers in the blood and are mostly stored in the bone marrow and spleen.
Through degranulation and via neutrophil extracellular traps (NETs).
Round nucleus, minimal cytoplasm, usually no granules
Immunophenotypic analysis is the use of antibodies directed against CD markers to phenotype cells.
These markers are involved in binding antigens and CD21 acts as a receptor for EBV.
CALT stands for conjunctiva-associated lymphoid tissue.
It is the necessary secondary signal delivered by co-stimulatory molecules that helps to activate T cells.
The white pulp is analogous to the lymph node, where immune cells are arranged in nodules and it plays a major role in mounting adaptive immune responses against antigens in the blood.
The gastric pH is approximately 3.0.
Through granulopoiesis at a rate of 5 × 10^10 per day.
Neutrophils (pink), Eosinophils (red-orange), Basophils (blue)
2-10%
Flow cytometry and microscopy, using immunohistochemistry (IHC) and immunofluorescence (IF).
Macrophages express Fc and C3b receptors.
Peyer's patches are organized lymphoid follicles located in the small intestine, part of GALT.
They participate in FcR binding with IgE, leading to degranulation and the release of inflammatory mediators.
Cromolyn and Diphenhydramine are examples.
Salivary glands contribute to mucosal immunity by producing secretory IgA and other immune factors.
They limit the ability of mast cells and basophils to degranulate, preventing the release of histamine and inflammatory mediators.
Waldeyer’s ring consists of palatine and adenoid tonsils and plays a crucial role in immune defense in the oral and pharyngeal regions.
They secrete cytokines that help with immune response against various pathogens and function as antigen-presenting cells (APCs).
Phagocytic killing, antigen processing and presentation, co-stimulation, and cytokine delivery.
They secrete cytokines to promote T cell activation and differentiation.
