Immunology is the study of the immune system.  The immune system protects us from infection through various lines of defense.  Molecular and cellular components make up the immune system.  The function of these components is divided into non specific mechanisms, those which innate to an organism, and responsive responses which are adaptive to specific pathogens.  Fundamental or classical immunology involves studying the components that make up the innate and adaptive immune system.

Innate immunity is the first line of defense and is non-specific that is the responses that are the same for all potential pathogens, no matter how different they maybe.  Innate immunity includes physical barriers( e.g. skin, saliva etc) and cells (e.g. macrophages, neutrophils, basophils, mast cells etc).  These components are ready to go and protect an organisms for the first few days of infection.  Adaptive immunity is the second line of defense which involves building up memory of encountered response specific to the pathogen or foreign substance.

Adaptive immunity involves antibodies, which generally target foregin pathogens roaming free in the bloodstream.   Also involved are T-cells, which are directed especially towards pathogens that have colonized cells and can directly kill infected cells or help control the antibody response.