Question

Type a 500-600 word response to this topic below:

The B cell response is largely associated with the generation of a tailored antibody response to combat pathogens. This involves a number of steps from the naive B cell’s from first encounter with antigen to becoming an antibody secreting plasma cell, secreting high affinity antibody of a useful isotype.

With this general theme in mind, paint a picture in word of the processes and interactions that occur in secondary lymphoid organs that result in the generation and secretion of high affinity, isotype switched antibodies.

Answer 1

*B cells in circulation comprise about 10-15% of lymphocytes.

*Origin and central organ are same -->Bone marrow

*B cells are present at
Lymph node of cortex
White pulp of spleen
MALT mucosa associated lymphoid tissue of ileum

*B cells are unique, as they are the only APCs(Antigen presenting cells) that specifically recognize antigen via the B cell receptors (of surface bound antibody).

*Depending upon the maturation stage of B cells, specific CD molecules appear on the cell surface which can be identified by CD markers.

*Common B cell markers are:
CD 19, 20, 21, 23.

*These cells also possess B cell receptors (BCR) for surface immunoglobulins (IgM and IgD ) on all mature and naive B cells and Fc receptor for attaching to antibody molecule.

*They are antigen binding component of B cell receptor complex .

*On coming in contact with antigen (e.g. invading microorganims), B cells are activated to proliferate and transform into plasmacytoid lymphocytes and then into plasma cells.

*Mechanism of activation of B cell activation
1.B cell receptor complex comtains Membranous IgM and IgD and associated signalling molecules IgBeta( CD79b)

Activation of B cells
1)T cell dependent activation

In this type of activation

a) First signal comes from antigen cross linking to B cell receptor .( BCR)
b) Second signal comes from costimulation by CD40L of T cell

B cells or Antigen presenting cells ( APC)
Ingest antigen protein into vesicles.

*Proteins are then digested into peptides and then it is presented to class MHC 2 protein .

*Peptide alomg with MHC 2 complex
molecules are recognised by Helper T cells and CD40 L on B cells CD40 receptor leading to B cell activation.This is Costimulatory signal for B cell .

*T cell help is provided to B cells by a subset of T helper cells, TH 2, by elaborated interleukins (IL-4, IL-5, IL-10, IL-13).

*Th1 response induces B cells to make opsonizing (marking for phagocytosis) and complement-fixing antibodies.

*Th2 also produce Interleukin 4, which help to facilitates B cell isotype switching.

*Also B cells 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 .