Factors influencing immunogenicity
Innate immunity
| Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells that attack foreign cells in the body. The innate immune response is activated by chemical properties of the antigen. |
Adaptive immunity
| Adaptive immunity refers to antigen-specific immune response. The adaptive immune response is more complex than the innate. The antigen first must be processed and recognized. Once an antigen has been recognized, the adaptive immune system creates an army of immune cells specifically designed to attack that antigen. Adaptive immunity also includes a "memory" that makes future responses against a specific antigen more efficient. |
2. What types acquired immunity do you know?
Active Immunity
Antibodies are produced by the body in response to infection
Naturally Acquired Active Immunity
Antibodies are formed in the prescence of active infection in body - Duration: lifelong
Artificially Acquired Active Immunity
Antigens (vaccines/toxoids) are administered to the person to stimulate antibody production - Duration: many years
Passive Immunity
Antibodies are produced by another source, animal or human
Naturally Acquired Passive Immunity
Antibodies are transferred naturally from an immune mother to her baby through breast milk/placenta - Duration: 6 mos to 1 yr
Artificially Acquired Immunity
Immune serum (antibody) from another human/animal is injected - Duration: 2-3 wks.
3. Give the characteristic of antigen-presenting cells; Recognize the significance of the immune system in combating infection and disease;
An antigen-presenting cell (APC) or accessory cell is a cell that displays foreign antigens complexed with major histocompatibility complexes (MHCs) on their surfaces; this process is known as antigen presentation. T-cells may recognize these complexes using their T-cell receptors (TCRs). These cellsprocess antigens and present them to T-cells.
Antigen-presenting cells fall into two categories: professional and non-professional.
T cells cannot recognize, and therefore cannot respond to, 'free' antigen. T cells can only 'see' an antigen that has been processed and presented by cells via carrier molecules like MHC and CD1 molecules. Most cells in the body can present antigen to CD8+ T cells via MHC class I molecules and, thus, act as "APCs"; however, the term is often limited to specialized cells that can prime T cells (i.e., activate a T cell that has not been exposed to antigen, termed a naive T cell). These cells, in general, express MHC class II as well as MHC class I molecules, and can stimulate CD4+ ("helper") T cells as well as CD8+ ("cytotoxic") T cells, respectively.
To help distinguish between the two types of APCs, those that express MHC class II molecules are often called professional antigen-presenting cells.
Professional
Professional APCs are very efficient at internalizing antigens, either by phagocytosis or by receptor-mediated endocytosis, and then displaying a fragment of the antigen, bound to a class II MHC molecule, on their membrane. The T cell recognizes and interacts with the antigen-class II MHC molecule complex on the membrane of the antigen-presenting cell. An additional co-stimulatory signal is then produced by the antigen-presenting cell, leading to activation of the T cell. The expression of co-stimulatory molecules is a defining feature of professional APCs.
There are three main types of professional antigen-presenting cells:
· Dendritic cells (DCs), which have the broadest range of antigen presentation, and are probably the most important APC. Activated DCs are especially potent THcell activators because, as part of their composition, they express co-stimulatory molecules such as B7. This B7 co-stimulator of mature interdigitating dendritic cell (IDC) interacts with surface CD28 of naïve T-cell.
· Macrophages
· Certain B-cells, which express (as B cell receptor) and secrete a specific antibody, can internalize the antigen, which bind to its BCR and present it incorporated to MHC II molecule, but are inefficient APC for most other antigens.
· Certain activated epithelial cells
Non-professional
A non-professional APC does not constitutively express the Major Histocompatibility Complex class II (MHC class II) proteins required for interaction with naive T cells; these are expressed only upon stimulation of the non-professional APC by certain cytokines such as IFN-γ. All nucleated cells express the Major Histocompatibility Complex class I necessary to be considered a non-professional APC. As erythrocytes do not have a nucleus, they are one of the few cells in the body that cannot display antigens.
4. Describe the factors influencing immunogenicity; Compare the structures of T-independent and T-dependent antigens;
FACTORS INFLUENCING IMMUNOGENICITY