Vaccines are prepared from immune

$A$ : Vaccine against $AIDS$ has not been made inspite of repeated attempts.
$R$ : $HIV$ has the ability to get mutated to form several subtypes.

The secondary host of malaria parasite is

T-lymphocyte is produced in

Cirrhosis is

During an allergic reaction, the binding of antigens to IgE antibodies initiates a response, in which chemicals cause the dilation of blood vessels and a host of other physiological changes. Such chemicals are