Question

Describe the process by which a dose of microorganisms entering the body through a cut in the skin progresses through innate immune activation and recognition by the adaptive immune system, up to the point of T and B cell activation. Please discuss where this process occurs, and how the structure of the tissue it occurs in is relevant to the process. Address the problem of maximizing the chance that antigen will come into contact with the relevant antigen binding T or B cell.

Answer 1

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 .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. 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 II 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 Lymoh 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.