ACQUIRED IMMUNITY RECOGNITION

ADAPTIV IMMUNITY IS TRANSFERABLE Antibodies, antibody specificity, diversity Antibodies were discovered in the late 1800s (Emil Behting, Shibasaburo Kitasato) SERUM THERAPY antibodies specific to toxins Discovery of blood group antigens (Landsteiner) QUESTION: How can so many different pathogens and other structures be recognized by antibodies? What drives and How the production of antibodies? Niels Jerne Macferlene Burnet Ehrlich Paul

Macfarlane Burnet (1956 - 1960) CLONAL SELECTION THEORY What is a clone in fact? Antibodies are natural products that appear on the cell surface as receptors and selectively react with the antigen Lymphocyte receptors are variable and carry various antigen-recognizing receptors ‘Non-self’ antigens/pathogens encounter the existing lymphocyte pool (repertoire) Antigens select their matching receptors from the available lymphocyte pool, induce clonal proliferation of specific clones and these clones differentiate to antibody secreting plasma cells The clonally distributed antigen-recognizing receptors represent about ~107 – 109 distinct antigenic specificities

DIVERSITY OF LYMPHOCYTES 1012 lymphocytes in our body ( B and T lymphocytes) How many SPECIFICITIES ? Assumption 1 (Lamarcian) The receptor can be activated by many different antigens Assumption 2 (Darwinian) All lymphocytes have a different receptor Cc. (minimum) 10 million various (107) B lymphocyte clones with different antigen-recognizing receptors Cc. (minimum) 10 – 1000 million various (107 - 9) T lymphocyte clones with different antigen-recognizing receptors

BINDING OF ANTIGEN TO THE SELECTED B-LYMPHOCYTES RESULTS IN CLONAL EXPANSION B cell B Cell Receptor (BCR) Ag Differentiation Plasma cell ACTIVATION Clonal expansion Antibody (immunoglobulin Ig) secretion MEMORY B CELLS

Clonal selection induces proliferation and increases effector cell frequency No. of cell divisions No. of cells with useful specificity Threshold of protective effector function

POSSIBLE FATES OF B-LIMPHOCYTE CLONES Transient, not final differentiation state Activation Clonal expansion/proliferation Differentiation Plasma cell Antibody production Circulation Restricted life span Homeostasis Apoptosis Memory cell

Antigen recognizing receptor THE B-CELL ANTIGEN RECOGNIZING RECEPTOR AND ANTIBODIES PRODUCED BY PLASMA CELLS HAVE THE SAME PROTEIN STRUCTURE = IMMUNOGLOBULIN B CELL Antigen recognizing receptor BCR Immunoglobulin (Ig) Antibody

TWO FORMS OF IMMUNOGLOBULINS a a TWO FORMS OF IMMUNOGLOBULINS Membrane-bound Ig Antigen-specific receptor Antigen binding H L H L Secreted Ig Antigen-specific soluble protein EFFECTOR MOLECULE b a signalling B CELL PLASMA CELL

IMMUNOGLOBULIN IgG VH FV= VH+ VL VL Antigen binding site

Bacteria are not well informed how to display Ag determinants for proper binding by host-antibodies host-antibodies need to be flexible

TIME COURSE OF THE ADAPTIVE IMMUNE RESPONSE Days Antibody g/ml serum Antigen A Recognition Activation AFFERENT Lag Response to antigen A Antigen B Primary Response to antigen B A antigén

Rapid, prompt response (hours) No variable receptors NATURAL/INNATE Rapid, prompt response (hours) No variable receptors Limited number of specificities No improvement during the response No memory Not transferable Can be exhausted, saturated CHARACTERISTICS OF INNATE AND ACQUIRED IMMUNITY ADAPTIVE/ACQUIRED Time consuming Variable antigen receptors Many very selective specificities Efficacy is improving during the response Memory Can be transferred Regulated, limited Protects self tissues COMMON EFFECTOR MECHANISMS FOR THE ELIMINATION OF PATHOGENS

ORGANIZATION AND STRUCTURE OF THE IMMUNE SYSTEM

ORGANIZATION AND STRUCTURE OF THE IMMUNE SYSTEM ORGANS OF THE IMMUNE SYSTEM LYMPHOID ORGANS GENERATION AND MIGRATION OF CELLS OF THE IMMUNE SYSTEM LYMPHOCYTE HOEMOSTASIS, RECIRCULATION THE ROLE OF LYMPHATICS IN THE TRANSPORTATION OF ANTIGENS INITIATION OF IMMUNE RESPONSE IN PERIPHERAL LYMPHOID ORGANS

ORGANIZATION OF THE IMMUNE SYSTEM T-lymphocytes Cellular immune response Helper Th Cytotoxic Tc Pathogens Allergens WALDEYER RING Tonsils, adenoids Palatinal, pharyngeal lingual and tubar tonsils Thymus Spleen Lymph nodes CENTRAL PRIMARY LYMPHOID ORGANS PERIPHERAL SECONDARY LYMPHOID ORGANS Blood circulation Lymph circulation Bone marrow Stem cells Lymphatic vessels Nyirokerek B-lymphocytes Antibodies Antigens

ORGANIZATION OF THE IMMUNE SYSTEM LYMPHOCYTES CONGREGATE IN SPECIALIZED TISSUES CENTRAL (PRIMARY) LYMPHOID ORGANS Bone marrow Thymus DEVELOPMENT TO THE STAGE OF ANTIGEN RECOGNITION PERIPHERAL (SECONDARY) LYMPHOID ORGANS Spleen Lymph nodes Skin-associated lymphoid tissue (SALT) Mucosa-associated lymphoid tissue (MALT) Gut-associated lymphoid tissue (GALT) Bronchial tract-associated lymphoid tissue (BALT) ACTIVATION AND DIFFERENTIATION TO EFFECTOR CELLS BLOOD AND LYMPH CIRCULATION Lymphatics – collect leaking plasma (interstitial fluid) in connective tissues Lymph – cells and fluid No pump – one way valves ensure direction – edema Several liters (3 – 5) of lymph gets back to the blood daily – vena cava superior

CENTRAL (PRIMARY) LYMPHOID ORGANS

GENERATION OF BLOOD CELLS BONE MARROW TRANSPLANTATION BEFORE BIRTH AFTER BIRTH Yolk sac Flat bones Liver Cell number (%) Spleen Tubular bones years months BIRTH BONE MARROW TRANSPLANTATION

Őssejtek felfedezése Till és McCullogh 1960 Spleen of irradiated mouse Injected with bone marrow cells Colony forming units (CFU)

T cell precursors migrating to the thymus THE BONE MARROW HSC cell: assymetric division 7-8000/day self renewal B-precursor 2-3x108 Dendritic cell B-cell precursors Stem cell Stromal cell Bone Pre-B 2-3x107 T cell precursors migrating to the thymus 2x107 B-cell 1-3x106 Central sinus Mature naive B-lymphocytes

„Niche”-s provide the appropriate microenvironment for hematopoiesis HSC hematopoietic stem cells Entothel soluble factors(SCF, GM-CSF etc) adhesion mol. (VCAM, ICAM, E-selectin.), CXCL12 Mesenchimal cells MSC (stroma) CXCL12, nestin + cells HSC maintenance fenntartása (50% HSC ha KO) CAR sejtek (CXCL12 abundant reticular cells) Makrofágok Reg. of Osteogenesis, maintenance of HSC Adipocytes negative regulators Trabecular bone osteoblast provide growth factors and adhesion molecules

Haematopoietic stem cell niches Figure 1 | Haematopoietic stem cell niches. In the bone marrow, haematopoietic stem cells (HSCs) can be found near the endosteal surface (a); in association with CXCL12‑abundant reticular (CAR) cells (b); and in the periphery of sinusoids and perivascular nestin-expressing cells (c). Each niche is thought to provide signals that support HSC behaviour, although the relationship between HSCs that are present in different niches is still unclear (dotted arrows). Likewise, blood vessels in the bone marrow are often in close association with bone, although their interaction is still poorly understood (d). At the endosteal surface, osteoblastic cells express factors that participate in HSC retention; osteoclasts regulate osteoblastic cell function by inducing bone remodelling; and macrophages regulate osteoblastic cell activity and the retention of HSCs. In the bone marrow stroma, HSCs are associated with CAR cells, which express factors that promote HSC retention. Adipocytes negatively regulate HSCs in the steady state. In the perivascular area, HSCs are associated with nestin-expressing cells, which promote HSC retention and are regulated by macrophages and the sympathetic nervous system (SNS). FE. Mercier Nat Rev Immunol 2012

| Immune cell niches. During B cell differentiation Figure 2 | Immune cell niches. During B cell differentiation, haematopoietic stem cells (HSCs) and pre-pro‑B cells are found in close association with CXCL12‑abundant reticular (CAR) cells (a), whereas pro‑B cells are more often in contact with interleukin‑7 (IL‑7)-secreting stromal cells (b). Later in B cell development, a population of immature B cells can be found in close association with endothelial cells (c). Naive B and T cells, which can respond to blood-borne pathogens, are found within a perivascular niche that is constituted by a network of dendritic cells (DCs) (d). Bone marrow-resident memory CD4+ T cells reside next to IL‑7-secreting stromal cells and are mostly found in a quiescent state (e). Plasma cells also reside in the bone marrow. CAR cells, eosinophils and megakaryocytes express factors that promote plasma cell engraftment and survival (f).

Adamo et al., Nature 2009, North TE, et al. Cell 2009 Biomechanical stress HSC recruitment Adamo et al., Nature 2009, North TE, et al. Cell 2009

Scheme of B Cell Development in the Bone Marrow Immature & mature B Central Sinus E n d o os t e u m Progenitors Pre-B X Stromal cells X X Macrophage

HEMATOPOIETIC STEM CELL BONE MARROW HSC HEMATOPOIETIC STEM CELL MYELOID PRECURSOR THYMUS B-cell LYMPHOID PRECURSOR NK-cell T-cell DC neutrophil monocyte mast BLOOD BLOOD TISSUES LYMPHOID TISSUES neutrophil B-cell T-cell mast mackrophage DC

STRUCTURE OF THE THYMUS Mature naive T- lymphocytes Capsule Septum Blood circulation Epithelial cells Thymocytes Dendritic cell Macrophage Hassal’s corpuscle Mature naive T- lymphocytes

STRUCTURE OF THE THYMUS

THYMUS INVOLUTION 3 day-old infant 70 years old Starting at birth, the T-cellproducing tissue of the thymus is gradually replaced by fatty tissue. This process is called the involution of the thymus. The graph shows the percentage of thymic tissue that is still producing T cells at different ages. The micrograph in panel a shows a section through the thymus of a 3-day-old infant; the micrograph in panel b shows a section through the thymus from a 70-year-old person for comparison. Tissue is stained with hematoxylin and eosin (red and blue). Magnification x 20. 70 years old

REDUCED RESISTANCE TO INFECTION AND TUMORIGENESIS THYMUS INVOLUTION Up to puberty/adolescence the size of the thymus is increasing and naive T lymphocytes are produced in waves to ensure protective immune responses A sustained loss of tissue mass, cellularity and functionality of the thymus starts after puberty and lasts to middle age followed by a slower rate of involution extending to old age DN cells do not proliferate and differentiate Diversity of the TCR repertoire progressively becomes more limited The thymic tissue is replaced by fat deposits In old people naive peripheral T cells proliferate more extensively than those in younger individuals to compensate low cell numbers and reach their replicative limits earlier than in young people REDUCED RESISTANCE TO INFECTION AND TUMORIGENESIS Similar number of T cell progenitors to young individuals Limited IL-7 production, Bcl-2 expression and TCRβ rearrangement Replicative potential of thymic stromal cells is decreased The levels of nerve growth factor (NGF) secreted by medullary thymic epitelial cells (TEC) and IGF-1 produced by thymic macrophages decline