第四章 免疫应答

Key notes
1. Selection and activation of B cells
When antigen is introduced into an individual, B cells with receptors for that antigen bind and internalize it into an endosomal compartment, and process and present it on MHC class II molecules to helper T cells.
When introduced into an individual who has not previously encountered the antigen , a primary immune response will develop within 4-5 days . This response results initially in the production of IgM and then IgG or other antibody isotypes(同种 型抗体) directed toward the antigen, and has a duration（延续时间）and antibody isotype profile which depends on the the quantity of antigen introduced and its mode of entry.
MHC class Peptide derived from carrier protein presented in MHC class Ⅱ
Selection and activation of B cells
These B cells are triggered to proliferate, giving rise to clones of large numbers of daughter cells. Some of the cells of these expanding clones serve as memory cells, others differentiate and become plasma cells which make and secrete large quantities of specific antibody.
T helper cells with specific receptors for a peptide from Ag5 in MHC class II bind to this complex and stimulate this B cell to clonally expand and differentiate into memory B cells and plasma cells which produce soluble antibody to Ag5. In addition, direct T cell interaction with the B cell induces class switching, which depending on the type of helper cell (Th1 vs Th2) and the cytokines it secretes, will result in production of antibody of the IgG, IgA or IgE classes .
(免疫细胞识别抗原后活化、增殖、分化为效应细胞， 并通过其所分泌的抗体或细胞因子表现出一定生物学效 应的过程。)
immune response
• Characteristics
1. Self and nonself discrimination 2. Specificity（特异性） 3. Memory（记忆性）
cells which have differentiated to more responsive
memory B cells, resulting in a more rapid response and usually in IgG antibody production.
Key notes Responses are usually multiclonal
B cell growth and differentiation
T cell growth and differentiation
Reciprocal activation of T and B cells
Humoral immunity
5
3
2
1
4
2. Primary and memory responses
Cross-reactive responses
Similar or identical antigenic determinants are sometimes found in association with widely different molecules or cells. This cross-reactivity is important: (a) in protection against organisms with cross-reactive antigens; and (b) in autoimmune diseases induced by infectious organisms bearing antigens cross-reactive with normal self antigens (e.g. streptococcal infections which predispose to rheumatic fever).
Key notes
Primary and memory (secondary) responses
On first exposure to antigen, a primary immune response develops resulting in production of IgM
antibodies. This is usually followed by an IgG
保护效应 (免疫生理) 自己——不排己 非己——排异 损伤效应(免疫病理) 自己——排己 非己——不排异或高应答
Section 1
Section A. Humoral Immune Response
A1 the cellular basis of the antibody response
Key notes Selection and activation of B cells
Antigen introduced into an individual binds specifically to B cells with receptors for that antigen. In the presence of T cell help these B cells clonally expand (proliferate) and some differentiate into plasma cells which make antibody specific for the antigen triggering the response.
immune response within 4-5 days. This response is self limiting and will stop when antigen is no longer available to stimuled, there are more antigen specific B
Chapter Ⅳ
Immune response
immune response
• Definition immune response is a biological process mediated by the antibody or cytokines produced by immune cells which was activated after antigen recognition , then proliferate and differentiate into effector cells.
Immune response
• Type
Mechanism (根据发挥效应的机理) humoral immune response cell-mediated immune respons Introduced time of antigen (根据抗原进入体内的时间和次数) primary immune response Secondary immune response
Immune response
Effect(效应)
• Protective effect self——no rejection Non-self ——rejection and elimination • Detrimental effect self——rejection Non-self ——no rejection or overreact
Antibodies produced by a single cell are homogeneous, but the response to a given antigen involves many different specific antibody producing cells and thus, overall, is very heterogeneous (i.e. multiclonal). Moreover, the effectiveness of an antibody response to a microorganism may depend on this heterogeneity.