Question

Describe the mechanisms involved in cell-mediated immunity and humoral immunity

Week 3 Ticket to Class Lewis Chapter 13 1. Describe the mechanisms involved in cell-mediated immunity and humoral immunity (aka 2. Describe the 4 types of hypersensitivity reactions. Lewis Chapter 14 3. Explain the diagnosis criteria for acquired immunodeficiency syndrome (AIDS). 3 4 5 6 8

Answer 1

1. Mechanism of cell mediated immunity :-

- Activated T-cells start to proliferate , synthesize, and secrete interleukin -2 to the cell surface .

- After several divisions they differentiate to effector and memory T cells population .

- Memory T cells have longer life span and provide immunity ,if the person is re-exposed to the same antigen

In this the cytotoxic T-cells migrate to the site of invasion and bind to target cells bearing antigen complex and then destroy infected cells by secreting two substances :-

- perforin

- granzyme

# Mechanism of humoral immunity :-

- B lymphocytes recognise specific antigen . Proliferate and differentiate into antibody secreting plasma cells .

- Antibodies bind to specific antigens on microbes , destroy microbes via specific mechanism.

- Some B lymphocytes evolve into the resting state into memory cells.

2. The four types of hypersensitivity reactions are :-

a) Allergic hypersensitivity = it is type -1 ,IgE mediated reaction . It is quick onset after exposure . Examples are bee stings ,latex allergy certain medications .

b) Cytotoxic hypersensitivity = it is antibody mediated type 2 hypersensitivity . Examples are hemolytic reactions ,goods pasture syndrome ,hyperacute graft rejection.

C) Immune complex deposition = it is type 3 hypersensitivity . IgG and IgM mediated . Examples are hypersensitivity pneumonitis ,SLE etc.

d) Delayed or cell mediated immunity = it is type 4 hypersensitivity reaction. Examples are chronic graft rejection ,latex allergy ,nickel , PPD test etc .

3. The diagnostic criteria for AIDS established by the Center for disease control and prevention is that a person with HIV must have AIDS defining condition or have a CD4 count less than 200 cells / mm^{​​​​3}​​​​ .