<unk> is a medical term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion.<unk> involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of pathogens to stop infection by micro-organisms before they can cause disease. Other components of the immune system adapt themselves to each new disease encountered and are able to generate pathogen-specific<unk> 
Specific, or adaptive<unk> is often sub-divided into two major types depending on how the<unk> was introduced. Natural<unk> occurs through contact with a disease causing agent, when the contact was not deliberate, whereas artificial<unk> develops only through deliberate actions. Both natural and artificial<unk> can be further subdivided, depending on the amount of time the protection lasts. Passive<unk> is short lived, and usually lasts only a few months, whereas protection via active<unk> lasts much longer, and is sometimes life-long. The diagram below summarizes these divisions of<unk> 
A further subdivision of adaptive<unk> is characterized by the cells involved; humoral<unk> is the aspect of<unk> that is mediated by secreted antibodies, whereas the protection provided by cell mediated<unk> involves T-lymphocytes alone. Humoral<unk> is active when the organism generates it’s own antibodies, and passive when antibodies are transferred between individuals. Similarly, cell mediated<unk> is active when the organisms’ own T-cells are stimulated and passive when T cells come from another organism.
Immunity 
Intrinsic immunity
Biological system
Cellular memory
Autoimmunity
Symptom
Innate immune system
Fertility