How do the B-cells and T-cells recognize or distinguish a body cell from a foreign particle?
I suspect something to do with this causes Auto Immune Disorders.
Broad question. Summary:
The innate immune system processes everything. When it senses that something is dangerous it tells the adaptive immune system, that is T and B cells, that this thing I'm holding is dangerous (via coreceptors and cytokines).
T and B cells that are specific for this dangerous protein (or sometimes non-protein) are activated.
Ideally T and B cells that react to self proteins are deleted. These are from central tolerance mechanisms when the cells are developing (T and B cells are tested against self proteins; if they react they die) and in the periphery (once they're mature) by them only getting activated by the innate immune system and other mechanisms. There's also T regs which regulate the immune system by preventing any cells that react to self proteins from being activated.
Autoimmune disorders are caused by a break down of these mechanisms.
I often have to reiterate this question in my head to clarify to myself how it works, though I tend to take an approach that asks more: What is different between a part of the body and something foreign which triggers an immune response?
Here is the part that concerns B and T cells:
Aside from this, the main method by which B and T cells determine whether to activate or not is context, which means two things:
Both APCs and inflammation are mainly provided by parts of the innate immune system, adding another safety barrier with more recognition mechanisms to tell self from non-self.
Good answer Android. Recognition of self vs non-self is the central theme of immunology.
I wanted to clarify and kind of oversimplify a part of Android's response though... B Cells and T Cells get their antigen receptors made by DNA rearrangement as immature cells. This is a random process and leads to receptors capable of binding (theoretically) anything. As these cells are developing in controlled environments, anything they see is 'self'. If they react to these 'self' antigens, the cells are eliminated. Later in life, antigen receptor activation turns from a self-eliminating event into an activating event. If all goes well, this mature population has already been screened for anti-self cells, so anything that activates them is assumed to be foreign and therefore a threat.