In: Anatomy and Physiology
Immune System and Lymphatic System
When the foreign antigen enters the body the body removes the antigen via 2 Types of immunity
1) Innate Immunity 2) Adaptive Immunity
1)When the microbes enter through skin first
innate immunity try to eliminate it as skin act as
barrier because it is made up of many layers .
Also Phagocytic cells like neutrophils
Natural killer cells complement
system ,Toll like recetors all of them try to eliminate the
bacteria by innate system that is present since birth .
When innate immunity fails to eliminate the pathogen then adaptive
immunity comes into play .
2)The critical first step in the elicitation of the adaptive immune
response to a primary antigen is the processing of antigen by
antigen presenting cells (APC) for the presentation to naive T
lymphocytes. MHC 1 complex present on all nucleated cells
and its main function is to present tha antigen via Antigen cells
To cytotoxic cells .Professional
antigen-presenting cells (APCs) include ,
macrophages, and B
cells,Dendrites their main
function is to load partially degraded peptides into the groove of
the MHC class 2
molecules.
A).Dendritic cells - are the most important APCs, as they do not have to be activated in order to present antigen to T cells. They constitutively express the co-stimulatory molecules needed to activate the naive T helper cells.
B).Macrophages - help activate the Th1 response by digesting microbes and presenting them to the T cells to elicit a cell-mediated immune response
C).B cells- present specific protein antigens to T cells to help elicit a humoral immune response and form clonal proliferation of antibodies or a Th2 response. B cells are unique, as they are the only APCs that specifically recognize antigen via the B cell receptors (of surface bound antibody).
3)Once antigen is processed and presented to a T cell, the adaptive immune response is initiated. These interactions occur within the secondary lymphoid tissue ( Spleen ,MALT mucosa associated lymohoid tissue and Lymph nodes ).The purpose of these interactions is to generate effector cells, which will ultimately result in the elimination of the infection. In order to generate specific effector cells, the activation of T cells via the TCR must go through several checkpoints to ensure antigen specificity and eventual T-cell activation.
4)Two most important interactions occuring which act as gate
signals for activation of adaptive immune system .
1.First (primary) signal: recognition of the MHC:peptide complex by
the T cell receptor and coreceptors (CD4 and CD8)
2.Second (costimulatory) signal: recognition of B7 by CD28
5)Also Helper T cells are arguably the most important cells in adaptive immunity, as they are required for almost all adaptive immune responses. They not only help activate B cells to secrete antibodies and macrophages to destroy ingested microbes, but they also help activate cytotoxic T cells to kill infected target cells.
6)The Th1 response is characterized by the production of Interferon-gamma, which helps in activation of the bactericidal activities of macrophages and it also , and induces B cells to make opsonizing (marking for phagocytosis) and complement-fixing antibodies, and leads to cell mediated immunity .Th1 responses are more effective against intracellular pathogens (viruses and bacteria that are inside host cells). and foreign cells .
Th2 also produce Interleukin 4, which help to facilitates B cell
isotype switching.
The Th2 response help to release of Interleukin 5, which induces
eosinophils and act against parasites . In general, Th2 responses
are more effective against extracellular bacteria, parasites
including helminths and toxins.
Like cytotoxic T Lymphocytes , most of the helper
T Lymphocyte die after the infection is subsided
and form memory cells which helps during further infection.
Also B lymphocyte produce many antibodies
against bacteria and help to get rid of infection .
IgM first antibody to produce
IgD attaches to Bcell and activate it
igG Opsonisation
IGA mucosal immunity Respiratory and GiT
IgE In allergic mast
cell mediated reactions .