• All cells have proteins and other substances projecting from their cell membrane
• These are known as?antigens?and are?specific?to that type of cell
• Lymphocytes have the ability to ‘read’ the antigens on the surfaces of cells and recognise any that are foreign
• They then make?antibodies?which are a?complementary shape to the antigens?on the surface of the pathogenic cell

Antigens and antibodies

• The antibodies attach to the antigens and cause?agglutination?(clumping together)
• This means the pathogenic cells cannot move very easily
• At the same time,?chemicals?are released that signal to?phagocytes?that there are cells present that need to be destroyed

Agglutinated pathogens cannot move easily

• The?initial response?of a lymphocyte encountering a pathogen for the first time and making specific antibodies for its antigens can take?a few days, during which time an individual may get sick
• Lymphocytes that have made antibodies for a specific pathogen for the first time will then make ‘memory cells’ that retain the instructions for making those specific antibodies for that type of pathogen
• This means that, in the case of reinfection by the same type of pathogen,?antibodies can very quickly be made?in greater quantities and the pathogens destroyed before they are able to multiply and cause illness
• This is how people can become?immune?to certain diseases after only having them once
• It does not work with all disease-causing microorganisms as some of them?mutate?fairly quickly and change the antigens on their cell surfaces
• Therefore, if they invade the body for a second time, the memory cells made in the first infection will not recall them as they now have slightly different antigens on their surfaces (e.g. the cold virus)

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