Our first line of defence against foreign organisms is barrier tissues such as the skin that stop the entry of organism into our bodies. If, however, these barrier layers are penetrated, the body contains cells that respond rapidly to the presence of the invader. These cells include macrophages that engulf foreign organisms and kill them without the need for antibodies. Immediate challenge also comes from soluble molecules that deprive the invading organism of essential nutrients (such as iron) and from certain molecules that are found on the surfaces of epithelia, in secretions (such as tears and saliva) and in the blood stream. This form of immunity is the innate or non-specific immune system that is continually ready to respond to invasion.
A second line of defence is the specific or adaptive immune system which may take days to respond to a primary invasion (that is infection by an organism that has not hitherto been seen). In the specific immune system, we see the production of antibodies (soluble proteins that bind to foreign antigens) and cell-mediated responses in which specific cells recognize foreign pathogens and destroy them. In the case of viruses or tumours, this response is also vital to the recognition and destruction of virally-infected cells. The response to a second round of infection is often more rapid than to the primary infection because of the activation of memory B and T cells.
The B and T type lymphocytes make up the immune response. T cells have receptors on their surface that recognise particular antigens e.g. pathogen, that triggers a response from the body's immune system. T cells attach to a particular antigen and then destroy the cell which has that antigen.
B cells secrete antibodies which are specific to a particular antigen. Once a T cell has spotted an antigen, it gives a signal to B cells to multiply and make a big population of identical cells to secrete lots of identical antibodies to fight the infection.
Memory B cells stay around in the blood after the original infection has been fought. They can reproduce very fast if the same antigen enters the body for a second time. That’s why we are immune to most diseases if we've already had them. The body carries a 'memory' of what the antigen was like, so it can produce loads of antibodies to kill the infection easily if we get infected again. E.g. Breast milk contains antibodies to make the baby pre- immune to some diseases.
The following is a diagram showing what phagocytes and what lymphocytes do:
Phagocytes can engulf microbes (i.e. micro organisms) lymphocytes produce antibodies as part of the immune system
and digest them.
Vaccination protects against viruses- vaccination involves injecting dead or weakened virus materials into the body. The body's lymphocytes react by producing anti bodies as shown by the diagram above. If live viruses infect the body later on, they are battled immediately. The body 'remembers' antibodies it's made before. Memory B cells trigger speedy production of antibodies to destroy the viruses.
In the UK, vaccinations are often given to children at a young age e.g. the MMR (Measles, Mumps, and Rubella) vaccine that there has been a bit of publicity about recently. If someone is infected with a dangerous pathogen e.g. some types of rabies, ready made antibodies are injected to combat the infection straight away.
Careers in Immunology Immunologists are always in demand in Universities, Research Institutes and the pharmaceutical and biotechnology industries. For a research career a PhD is a necessary postgraduate qualification although a BSc in Immunology is also a suitable qualification for working at Research Assistant level in research laboratories in academia or industry, diagnostic labs in the healthcare sector and any number of allied posts. Several graduates choose to enter Medical School
Entry requirements
A/AS Levels: Normally applicants are expected to have three GCE A levels including Biology and preferably one from Chemistry, Physics or Mathematics. General Studies not accepted.
Typical offer: BBC at A2 (tariff range 280-340 points) Key Skills are welcomed in addition and may be included in any offer.
GCSE: Mathematics, Chemistry and English required if not held at A2/AS level.
Access to HE course: Pass kite-marked course with a substantial number of credits at level 3, normally minimum 18.
European Baccalaureate: Pass with 70% overall.
International Baccalaureate: Pass Diploma with 32-34 points.