Answer:
The immune system is compromised of three different 'layers'; which are barrier immunity, innate immunity, and acquired (adaptive) immunity. Barrier immunity is typically thought of as the skin. The skin contains immune cells, secretes antimicrobial proteins, and can mechanically protect against foreign invaders by desquamation (shedding skin). However, barrier protection can also be found in the nose, pharynx, gi epithelium, and respiratory epithelium. A good example of this would be the cilia in respiratory epithelium that only direct foreign bodies up from the lower lobe up to the trachea.
Now onto your specific question, which pertains to the next two barriers of immunity. If something is able to pass the barrier immunity and successful enters our body, then the innate immunity will kick in. The innate immune system is compromised of varying cells such as: monocytes, DCs, neutrophils, basophils, eosinophils, lymphoid cells (including NK cells). These cells typical will start to develop in the 5th week of gestation in a normal person. If the innate immunity is not the answer to your problems then the adaptive system will kick in. This system is compromised of lymphocytes, more specifically T cells and B cells. Adaptive immunity is developed throughout life starting in early childhood, as you are exposed to the world. Developing neonatal adaptive immunity is a widely talked about subject in medicine as it can be developed, but it seems that there is not long lasting immunity.
The general differences between the two are as follows:
Innate:
-fast acting
-response is none targeted
-no more of germs killed in past
-comprised of neutrophils and macrophages
Adaptive:
-slow to respond
-Antibodies act against specific targets
-antibodies remember past germs
-antibodies are created by T cells and B cells
Hope this helps! If not send a message. :)