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Name : Uroosa Naeem Qureshi
Father Name: Muhammad Naeem Qureshi
rd
Semester Evening 2
nd
Year
Assignment no: 2 Immune system with Innate and Adaptive Immune System
Course: Microbiology
Maam Beneesh Asghar
Introduction Of Immune system : Our immune system is essential for our survival. Without an immune system, our bodies would be open to attack from bacteria, viruses, parasites, and more. It is our immune system that keeps us healthy as we drift through a sea of pathogens. The complex group of defense responses found in humans and other advanced vertebrates that helps repel disease-causing organisms (pathogens). Immunity from disease is really conferred by two cooperative defense systems, called nonspecific, natural immunity and specific , immunity. Nonspecific protective mechanisms repel
all microorganisms equally, while the precise immune responses are tailored to particular sorts of invaders. Both systems work together to thwart organisms from entering and proliferating within the body. These immune mechanisms also help eliminate abnormal cells of the body which will become cancer. immune stimulation by activated helper T cells Stimulation of immune reaction by activated helper T cells. Activated by complex interaction with molecules on the surface of a macrophage or another antigen-presenting cell, a helper T cell proliferates into two general subtypes, TH1 and TH2. These successively stimulate the complex pathways of the cell-mediated immune reaction and therefore the humoral immune reaction , respectively. system is usually divided into two categories--innate and adaptive--although these distinctions aren't mutually exclusive.
protects the extremely vital and sensitive system nervous from pathogens that have already gained access to the host's body).
Adaptive immunity :
Adaptive immunity refers to antigen-specific immune reaction. The adaptive immune reaction is is more complex than the innate. The antigen first must be processed and recognized. Once an antigen has been recognized, the adaptive system creates a military of immune cells specifically designed to attack that antigen. Adaptive immunity also includes a "memory" that creates future responses against a selected antigen more efficient. more complex than the innate. The antigen first must be processed and recognized. Once an antigen has been recognized, the adaptive system creates a military of immune cells specifically designed to attack that antigen. Adaptive immunity also includes a "memory" that creates future responses against a selected antigen more efficient. The major functions of the acquired system include:
- Recognition of specific "non-self" antigens within the presence of "self", during the method of antigen presentation.
- Generation of responses that are tailored to maximally eliminate specific pathogens or pathogen-infected cells.
- Development of immunological memory, during which pathogens are "remembered" through memory B cells and memory T cells.
Lymphocytes:
The cells of the acquired system are T and B lymphocytes; lymphocytes are a subset of leukocyte. B cells and T cells are the main sorts of lymphocytes. The physical body has about 2 trillion lymphocytes, constituting 20โ40% of white blood cells (WBCs); their total mass is about an equivalent because the brain or liver. The peripheral blood contains 2% of circulating lymphocytes; the remainder move within the tissues and system lymphaticum B cells and T cells are derived from an equivalent multipotent hematopoietic stem cells, and are morphologically indistinguishable from each other until after they're activated. B cells play an outsized role within
the humoral immune reaction , whereas T cells are intimately involved in cell-mediated immune responses. altogether vertebrates except Agnatha, B cells and T cells are produced by stem cells within the bone marrow T progenitors migrate from the bone marrow to the thymus where they're called thymocytes and where they become T cells. In humans, approximately 1โ2% of the lymphocyte pool recirculates each hour to optimize the opportunities for antigen-specific lymphocytes to seek out their specific antigen within the secondary lymphoid tissues In an adult animal, the peripheral lymphoid organs contain a mix of B and T cells in a minimum of three stages of differentiation:
- naive B and naive T cells (cells that haven't matured), left the bone marrow or thymus, have entered the systema lymphaticum , but have yet to encounter their cognate antigen,
- effector cells that are activated by their cognate antigen, and are actively involved in eliminating a pathogen.
- memory cells โ the survivors of past infections.
Antigen presentation:
Acquired immunity relies on the capacity of immune cells to differentiate between the body's own cells and unwanted invaders. The host's cells express "self" antigens. These antigens are different from those on the surface of bacteria or on the surface of virus-infected host cells ("non-self" or "foreign" antigens). The acquired immune reaction is triggered by recognizing foreign antigen within the cellular context of an activated dendritic cell. With the exception of non-nucleated cells (including erythrocytes), all cells are capable of presenting antigen through the function of major histocompatibility complex (MHC) molecules.[4] Some cells are specially equipped to present antigen, and to prime naive T cells. Dendritic cells, B-cells, and macrophages are equipped with special "co-stimulatory" ligands recognized by co-stimulatory receptors on T cells, and are termed professional antigen- presenting cells (APCs). Several T cells subgroups are often activated by professional APCs, and every sort of T cell is specially equipped to affect each unique toxin or microbial pathogen. the sort of T cell activated, and therefore the sort of response generated, depends, in part, on the context during which the APC first encountered the antigen.
Exogenous antigens:
Dendritic cells engulf exogenous pathogens, like bacteria, parasites or toxins within the tissues then migrate, via chemotactic signals, to the T cell-enriched lymph nodes. During migration, dendritic cells undergo a process of maturation during which they lose most of their ability to engulf other pathogens, and develop a capability to speak with T-cells. The dendritic cell uses enzymes to cut the pathogen into smaller pieces, called antigens. within the lymph gland , the dendritic cell displays these non-self antigens on its surface by coupling them to a receptor called the main histocompatibility complex, or MHC (also known in humans as human leukocyte antigen (HLA)). This MHC: antigen complex is recognized by T-cells passing through the lymph gland. Exogenous antigens are usually displayed on MHC class II molecules, which activate CD4+T helper cells.
Endogenous antigens :
Endogenous antigens are produced by intracellular bacteria and viruses replicating within a number cell. The host cell uses enzymes to digest virally associated proteins, and displays these pieces on its surface to T-cells by coupling them to MHC. Endogenous antigens are typically displayed on MHC class I molecules, and activate CD8+ cytotoxic T-cells. With the exception of non-nucleated cells (including erythrocytes), MHC class I is expressed by all host cells.
Helper T-cells
The T lymphocyte activation pathway. T cells contribute to immune defenses in two major ways: some direct and regulate immune responses; others directly attack infected or cancerous cells. CD4+ lymphocytes, also called "helper" T cells, are immune reaction mediators, and play a crucial role in establishing and maximizing the capabilities of the acquired immune reaction .These cells have no cytotoxic or phagocytic activity; and can't kill infected cells or clear pathogens, but, in essence "manage" the immune reaction , by directing other cells to perform these tasks. Helper T cell s express T cell receptors (TCR) that recognize antigen sure to Class II MHC molecules. The activation of a naive helper T-cell causes it to release cytokines, which influences the activity of the many cell types, including the APC (Antigen-Presenting Cell) that activated it. Helper T-cells require a way milder activation stimulus than cytotoxic T cells. Helper T cells can provide extra signals that "help" activate cytotoxic cells.
Th1 and Th2: helper T cell responses:
Classically, two sorts of effector CD4+ T helper T cell responses are often induced by knowledgeable APC, designated Th1 and Th2, each designed to eliminate differing types of pathogens. The factors that dictate whether an infection triggers a Th1 or Th2 type response aren't fully understood, but the response generated does play a crucial role within the clearance of different pathogens. The Th1 response is characterized by the assembly of Interferon-gamma, which activates the bactericidal activities of macrophages, and induces B cells to form opsonizing (marking for phagocytosis) and complement-fixing antibodies, and results in cell-mediated immunity. generally , Th1 responses are simpler against intracellular pathogens (viruses and bacteria that are inside host cells). The Th2 response is characterized by the release of Interleukin 5, which induces eosinophils in the clearance of parasites. Th2 also produce Interleukin 4, which facilitates B cell isotype switching.In general, Th2 responses are more effective against extracellular bacteria, parasites including helminths and toxins. Like cytotoxic T cells, most of the CD4+ helper cells die on resolution of infection, with a few remaining as CD4+ memory cells.
- Agglutination: Reduces number of infectious units to be addressed
- Activation of complement: Cause inflammation and cell lysis
- Opsonization: Coating antigen with antibody enhances phagocytosis
- Antibody-dependent cell-mediated cytotoxicity: Antibodies attached to focus on cell cause destruction by macrophages, eosinophils, and NK cells
- Neutralization: Blocks adhesion of bacteria and viruses to mucosa Like the T cell , B cell s express a singular B cell receptor (BCR), during this case, a membrane-bound antibody molecule. All the BCR of anybody just like B cells recognizes and binds to just one particular antigen. A critical difference between B cells and T cells is how each cell "sees" an antigen. T cells recognize their cognate antigen during a processed form โ as a peptide within the context of an MHC molecule, whereas B cells recognize antigens in their native form. Once a B cell encounters its cognate (or specific) antigen (and receives additional signals from a helper T cell (predominately Th2 type)), it further differentiates into an effector cell, referred to as a plasmacyte. Plasma cells are short-lived cells (2โ3 days) that secrete antibodies. These antibodies bind to antigens, making them easier targets for phagocytes, and trigger the complement cascade. About 10% of plasma cells survive to become long-lived antigen-specific memory B cells. Already primed to supply specific antibodies, these cells are often called upon to reply quickly if an equivalent pathogen re-infects the host, while the host experiences few, if any, symptoms.
