E 2.2 Immunological reactions of organism

Lecture 2.2 Immunological reactions of organism.

Plan:

1. Complement: A Versatile Backup System

Overall Stages in the Complement Cascade

3. Specific Immunity: The Adaptive Line of Defense

An Overview of Specific Immune Responses

Development of the Immune Response

System Cooperation in Immune Reactions to Antigens

The Role of Antigen Processing and Presentation

1. Complement: A Versatile Backup System Among its many overlapping functions, the immune system has another complex… Complement functions as a positive feedback loop or cascade reaction. Its primary action is a sequential physiological…

Overall Stages in the Complement Cascade

The final events in the complement series involve polymerization of C5b, C6, C7, and C8 into a half circular formation within the membrane (figure 1… Figure 1. Overview of the complement pathways. (a)All three pathways have different triggers and starting points, but…

An Overview of Specific Immune Responses

I.Development and differentiation of the immune system II.Lymphocytes, maturation, and the nature of antigens III.Cooperation between lymphocytes during antigen presentation

Development of the Immune Response System

Before we examine lymphocyte development and function in greater detail, we must initially review concepts such as the unique structure of molecules (especially proteins), the characteristics of cell surfaces (membranes and envelopes), the ways that genes are expressed, immune recognition, and identification of self and nonself. Ultimately, the shape and function of protein receptors and markers protruding from the surfaces of certain white blood cells are the result of genetic expression, and these molecules are responsible for specific immune recognition and, thus, immune reactions.

Figure 2. Overview of the origins and events of adaptive immune responses.

Cooperation in Immune Reactions to Antigens

The basis for most immune responses is the encounter between antigens and white blood cells. Microbes and other foreign substances enter most often through the respiratory or gastrointestinal mucosa and less frequently through other mucous membranes or the skin. Antigens introduced intravenously become localized in the liver, spleen, bone marrow, kidney, and lung. If introduced by some other route, antigens are carried in lymphatic fluid and concentrated by the lymph nodes. The lymph nodes and spleen are important in concentrating the antigens in areas where they will come in contact with antigen-presenting cells (APCs) and lymphocytes. APCs and lymphocytes can subsequently circulate into fluid compartments to seek out the antigens for which they are specific.

The Role of Antigen Processing and Presentation

Before a T cell can respond to APC-bound antigens, certain conditions must be met. T-cell-dependent antigens, usually proteinbased, require…

Figure 3. Interactions between antigen-presenting cells (APCs) and T helper (CD4) cells required for T-cell activation.

A few antigens can trigger a response from B lymphocytes without the cooperation of APCs or T helper cells. These T-cell-independent antigens are… Figure 4. Events in B-cell activation and antibody synthesis.*Only key receptors for these reactions are shown.