Question

Allergy sensitization - put these events in order #1-#4.

> Effector Th2 T cells interact with B cells to induce class switching to IgE

> Allergen is taken up by dendritic cells, processed, and presented to T cells to induce Th2 differentiation

> IgE is produced and binds to mast cells using FcE receptor

> IgE bound to mast cells binds allergen during a second (or later) encounter, leads to degranulation and allergy symptoms

Answer 1

The events for allergy sensitization take place in following manner: 2----->1----->3----->4

(2) Allergen is taken up by dendritic cells, processed, and presented to T cells to induce Th2 differentiation--------(1)Effector Th2 T cells interact with B cells to induce class switching to IgE----------->(3)IgE is produced and binds to mast cells using FcE receptor----------->(4)IgE bound to mast cells binds allergen during a second (or later) encounter, leads to degranulation and allergy symptoms

Explanation:

(2)Dendritic cells(DC), which are the most important antigen presenting cells  activate naive T cells. Dendritic cells are the reporters of the microenvironment if exposed to the allergen, migrate to the lymph nodes where they activate naive T lymphocytes.  In this case for allergies induce Type 2 helper T cell (Th2)-driven specific immune response towards allergens.

(1)There are two main components of the immune response leading to IgE production

• The first consists of the signals that favor the differentiation of naive TH0 cells to a TH2 phenotype.
• The second comprises the action of cytokines and co-stimulatory signals from TH2 cells that stimulate B cells to switch to producing IgE antibodies

Therefore for the case of allergins the effector Th2 cells stimulate B cells to induce class switching to IgE antibodies.

(3) IgE antibodies are primarily associated with allergy. Through their interaction with FcE receptors on mast cells and basophils, IgE antibodies in presence of antigen(allergin) induce release of histamine and other vasoactive substances.

(4) On binding of IgE the mast cells undergo degranulation and along with basophils release heparin, histamine and other effector substance to mediate immediate allergic attack.The mast cells along with basophils express high affinity IgE receptor and release chemical mediators that participate in immune and inflammatory response.