Immunology is concerned with immunity and all aspects
of the body's ability to resist infection and diseases
caused by pathogens (disease-causing organisms,
which are usually micro-organisms). Examples of
disease-causing organisms include viruses, bacteria,
protozoa or even larger parasites.
Note the relationship between Immunology
(concerning the body's ability to resist infection
and disease) and Pathology
(the study of disease processes including their
causes and characteristics.).