IMMUNE FUNCTION - 06/09/11
Résumé |
The extraordinary expansion in knowledge regarding immune function over the past 2 decades has resulted in an increased understanding and improved treatment of immunodeficiency disorders. Also, this progress has allowed for the recognition of the role of the immune system in many other diseases. The worldwide pandemic of the HIV infection during this same period has moved immunology into the daily practice of many practitioners. This article develops the basic principles that govern the immune system as it protects the host against a variety of foreign pathogens. This article provides a foundation for understanding the discussions of immunodeficiencies and the approaches used to treat these disorders.
Host defense consists of a phylogenetically more primitive innate immune system that acts as the initial defense against various pathogens and serves as a facilitator of specific immunity in higher organisms.5, 8, 19 This response depends heavily on phagocytic cells, and it is amplified by the complement system with the production of critical factors that enhance phagocytosis (i.e., opsonins) and attract cells to the site of inflammation (i.e., chemoattractants). The defense pathway that developed evolutionarily later in higher organisms is referred to as the adaptive immune system and involves a highly specific process of recognition and response to foreign substances (i.e., antigens), which requires lymphocytes and specialized antigen-presenting cells.1, 13 The adaptive response is initiated by lymphocytes encountering foreign antigen and depends on a combination of cell–cell interactions that generate humoral mediators, including immunoglobulins and potent bioactive hormones or cytokines that modulate the response.1, 13
The cellular components of the innate immune system consist of phagocytic cells (e.g., neutrophils, monocytes, and macrophages) and a population of lymphocytes. Neutrophils are mobile phagocytes that circulate in the blood ready to migrate to sites of inflammation.27 This process represents a one-way trip into affected tissues to deliver cells that are efficient in the ingestion and destruction of invading microorganisms. Macrophages, in contrast, are fixed tissue cells found in the reticuloendothelial system and other tissues. They provide critical phagocytic function for clearing antigenic substances from the blood as these materials circulate through the tissues. The ingestion of foreign antigens by both cell types is enhanced in the presence of specific antibody and complement components that are bound to the antigen surface. The innate immune system also interacts with components of a specific immune response by the production of cytokines.
The adaptive immune system is dependent on various lymphocyte subpopulations. Among these, the T cells represent the most prevalent lymphocytes in the circulation (
75%) and provides critical regulatory, memory, and cytotoxic effector (i.e., killer) cell function. The remainder of lymphocytes is divided approximately equally between B cells and natural killer (NK) cells. B cells ( 10–15%) secrete antibodies or immunoglobulins and are the principal effector cells for the humoral immune system. NK cells function at the interface between innate and adaptive immunity. These cells are capable of producing various cytokines that have a role in the development of an adaptive immune response. Also, NK cells function as “prearmed” cytotoxic cells that respond to certain virally infected and tumor targets.14
Plan
| Address reprint requests to Thomas A. Fleisher, MD Department of Laboratory Medicine Warren G. Magnuson Clinical Center National Institutes of Health 10 Center Drive MSC 1508 Bethesda, MD 20892–1508 |
Vol 47 - N° 6
P. 1197-1209 - décembre 2000 Retour au numéro
Article précédent
- PREFACE
- THOMAS A. FLEISHER, MARK BALLOW
- OFFICE EVALUATION OF CHILDREN WITH RECURRENT INFECTION
- Monika Woroniecka, Mark Ballow
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