Chapter 9 Inflammation and Immunity BIOL300

The chapter explains the innate immune response which functions without prior exposure to antigens. It includes various cellular defenses like natural killer cells and phagocytic cells, such as neutrophils and macrophages. In contrast, adaptive defenses involving B and T lymphocytes develop upon exposure to antigens and are more selective. The importance of physical barriers like skin and mucosal membranes is discussed, highlighting their antimicrobial molecules like defensins and cryptdins. Disruption of these barriers increases infection risk. The introduction to macrophages is made, emphasizing their role as phagocytes in clearing debris and dead cells and contributing to wound healing.

The lymphatic system's role in immunity is highlighted. It circulates lymph, rich in immune cells, through the body, cleaning debris. The white blood cells, derived from stem cells in red bone marrow, include neutrophils, lymphocytes, monocytes, eosinophils, and basophils, each having distinct roles. Neutrophils are vital for phagocytosis as part of the innate response, whereas lymphocytes distinguish between adaptive and innate responses. Eosinophils handle allergic reactions and parasitic infections, while basophils play a role in inflammation through histamine. Each leukocyte type's abundance in blood is also detailed.

Neutrophils, the most common leukocytes, are crucial in acute bacterial infections, releasing toxins and enzymes for combating pathogens but may also harm healthy tissue. Lymphocytes include T cells, B cells, and natural killer cells. T and B cells function in adaptive immunity responding to specific antigens, while natural killer cells are part of the innate defense. Differences in maturation locations for T and B cells are discussed, highlighting how thymus and bone marrow damage can affect these cells’ development. The division of T cells into helpers and cytotoxic classes is explained, focusing on their roles.

The significance of T helper and cytotoxic T cells in adaptive immunity is explored. T helper cells, with CD4 proteins, activate other immune cells by releasing cytokines, stimulating B cells and macrophages. Cytotoxic T cells with CD8 proteins destroy cells presenting certain antigens, aided by signals from helper T cells. The discussion includes how HIV targets CD4 positive cells, hindering the immune system's capacity to activate and respond robustly. B lymphocytes, with antibody-like receptors, play crucial roles in humoral immunity, producing memory cells for faster future responses and transforming into plasma cells to manufacture antibodies upon activation.

The function of complement proteins in the innate immune response is explained, including their role in inflammation and cell lysis. The formation of the MAC complex by complement activation is detailed, noting its method of lysing cells by creating membrane pores. Chemical mediators like kinins, influencing inflammation and vasodilation, are introduced. The endogenous mechanisms involving Hageman factor in both clotting and inflammation are discussed. Chemotactic cytokines are explained for their role in guiding immune cells to infection sites, illustrating the coordinated effort in innate immunity.

The inflammatory response's purpose of neutralizing threats and facilitating tissue repair is described. Both acute and chronic inflammation are explored, highlighting their characteristics and impacts on tissues, including the potential damage from excessive inflammation. The events of inflammation—vascular permeability increase, leukocyte migration, and phagocytosis—are linked to immune function. Diapedesis and chemotaxis processes enable leukocytes to reach inflamed tissues and contribute to pathogen clearance. The importance of redundant pathways in the immune system is acknowledged for robust defense.

The five cardinal signs of inflammation—redness, swelling, heat, pain, and loss of function—are explained, alongside their contributing factors like vasoactive chemicals and increased vascular permeability. These responses help dilute toxins, enhance immune cell delivery, and initiate healing. However, they can lead to tissue damage if excessive. The content covers inflammatory exudate's role in transporting immune components and facilitating tissue repair. Chemokines and cytokines' roles in immune cell migration and the nuances of leukocyte immigration from blood into tissues are explored in detail.

The process of phagocytosis by immune cells like macrophages and neutrophils involves engulfing pathogens into vesicles called phagosomes, which fuse with lysosomes to destroy the pathogen. Local inflammation symptoms can cause systemic effects such as fever, lethargy, and muscle catabolism. C-reactive protein serves as an indicator of acute inflammation, offering medical professionals a measurable marker. The narrative outlines the differences between innate and adaptive immune responses, emphasizing how memory B cells aid in faster secondary responses to pathogens previously encountered.

Differentiation of self from non-self by B and T cells is achieved through recognition of unique HLA markers, preventing the immune system from attacking self-cells. MHC proteins are categorized into Class I, II, and III, with Class I being crucial for antigen presentation in nucleated cells, while Class II is for phagocytic cells. These systems allow immune cells to recognize viral infections or foreign protein presence. The mechanism by which MHC Class I and II present antigens is described, along with their roles in initiating immune responses via helper T cells and cytotoxic T cells.

The specificity of T cells in recognizing antigens ensures the immune system's precision in targeting threats. Helper T cells activate other immune components, whereas cytotoxic T cells lead to cell lysis of infected cells. The interactions of these cells in HIV pathogenesis are explored, showing how HIV's targeting of CD4 cells disrupts immune signaling. The immune response's sophistication includes memory storage and activation of perforins by cytotoxic T cells to eliminate threats. Memory and effector roles in both B and T cells allow contingency against future infections, with perforins aiding in targeted degradation.

The section covers the types of antibodies, their structures, and functions. Immunoglobulins like IgG, IgM, IgA, IgD, and IgE are explained for their specific roles and occurrence in the body. Antibodies' abilities to neutralize antigens, promote phagocytosis, and activate complements are elaborated. The concept of class-switching in antibody production is discussed for its significance in immune adaptability, and how the presence of specific antibodies can indicate acute or chronic infection is outlined.