I have an interest in the immune system and I once bought the book Immune by Philipp Dettmer, who explained everything in a really fluid and comprehensive way. He gave some quick introduction to components and then introduced all of the main ideas through following the steps of the immune system responding to an infection. I will follow this and give most of the information in the basic overview through this format, to hopefully promote a cohesive understanding of this subject. To get a good well connected view i recommend reading the book.
Chemical and physical barriers of infection
Your body has some basic ways of defending itself from organisms. It has physical barriers and chemical barriers. These are things that stop most bacteria from getting a chance to establish themselves in a vulnerable nutrient rich environment where they can grow. The main example of a physical defence is the epithelia. This a layer of cells that is inbetween you and the outside world at every possible point. It changes form and type but it remains the same. It is your skin, your mucosa (gums and bodu lineing), and everything in between.
Your skin
This is your primary border between the outside world and your outside self. It has a few characteristics that enable it to be a durable, regenerating lining which separates you from everything else:
- It has a bonded layered structure (stratified) of keratinised skin cells which means the border is thick, tough and can regenerate.
- It is laden with chemical defenses which make living there rather difficult for bacteria to set up shop (and be first in line for skin breaks)
- These are sebacous gland secretion, which contain defensins and the like
- It possesses a microbial microbiome which makes it harder for other organisms to live there as well (think about trying to build a house and farm in an uninhabited area vs the middle of a city. There are less overall resources and space to grow)
Your mucosa
Your mucosa lines your inside border to the outside world (mouth throat gut all the way through to the anus). It is less durable, as it doesn’t have to resist rocks and abrasions and all that stuff, The inside of you is laden with microbes and so the mucosa is equipped to the teeth with chemical and immune defences. There is also commensal microbes in the gut which serve many more purposes than we are aware of. Some adaptations are:
- Acid in stomach
- mucous to trap organisms and debris
- spermine in semen
- lysozyme in tears nasal secretions and saliva
- etc
Components of the Innate immune system
Your innate immune system is your first line of defence. When there is a foreign body in your body it is the first to response and later on the brunt of the immune effectors. As it is the first to react it is not specific and is very general. There are 2 parts to it, cellular, and humoral (the proteins and antibodies which work to eliminate foreign bodies).
This is a complex system and there is lots of detail here
The cellular components are:
- Neutrophils
- Monocytes
- Basophils
- Eosinophils
- Mast cells
- Dendritic cells
- Natural killer cells
The humoral components are:
- Antibodies (many different types for each things)
- IgD
- IgA
- IgM
- IgE
- IgG
- Complement (this is whole system of interactive proteins) (this is also explained in the immunity to meningitis lecture)
Components of the adaptive immune system
This is the special weapons of your immune system which allows it to adapt to any organism present. They are involved in recognising antigens (bits of foreign bodies) and superchraging immune responses (T cells) and making antibodies to antigens (B Cells). There are only 2 cell types but within these types there is variation between Naive, activated and memory
The cells which make it up are:
- T cells
- Cytotoxic T cell (CD8+)
- naive
- activated
- memory
- Helper T cells (CD4+)
- naive
- activated
- memory
- Cytotoxic T cell (CD8+)
- B cells
- Naive
- Activated
- Plasma cells
- Memory
Communication and coordination
The needs to be a lot of back and forth for this system to function correctly. The communication happens through molecules which are called cytokines and these are released and received by various cells in your body. There can also be direct cell to cell communication through them touching each other.
Detection of foreign bodies (PRRs)
For your immune system to react to a foreign body (anything that is recognised as not of self, sometimes in autoimmunity stuff that is supposed to be there) It needs to sense said body, The adaptive and innate immune systems have different ways of doing this.
The innate immune has a certain class of receptors on its surface called pattern recognition receptors (for example Toll-like receptors). What these do is that they can recognise Pathogen-Associated Molecular Patterns (PAMPS) which are common components of pathogens, for example lipopolysaccharide is a common ingredient in bacterial cell walls and so the innate immune system readily reacts to it. The innate system can also recognise Danger Associated Molecule Patterns The adaptive immune system had different receptors which are much more comprehensive, as the immune system needs to respond to anything. I will explain this later
Acute inflammation
I will go through a scenario where there is an infection and acute inflammation
You stand on a nail and it punched through your shoe and skin, giving the bacteria on the sole of your foot and on the nail a nifty way to get through your previously insurmountable skin.
Once in your skin the bacteria begins to divide and multiple, as your body is full of nutrients and currently does not have much in the way of obstacles.
The resulting products of necrosis and the PAMPS released by the bacteria invading then alerts your innate immune system. The resident macrophages begin to phagocytose the bacteria, as well as send off cytokines that trigger acute inflammation. This involves mast cell degranulation releasing histamine and other signaller. This causes monocytes and neutrophils to marginate from the blood and enter the site of injury.
If there were just low virulence bacteria in the introduce species the innate immune system would be able to completely take care of the bacteria. For the sake of the learning experience lets say that there is a high virulence bacteria in the introduced species.
If this is the case then the innate immune system will not be able to eliminate the infection on its own and so the adaptive immune system will need to come into play
The dendritic cell is one of the bridges between the innate and adaptive immune system. It is at the initial site of infection and phagocytoses bacteria but not all the way. it keeps antigens within itself for presention. The dendritic cells then move nearby lymph nodes and begins presenting to naive T and B cells and when the T or B cell that matches the specific antigen is found it is activated with a certain ""handshake”. it then undergoes clonal expansion where it multiplies and travels to the site of infection. Here the T cells support the macrophages and the B cells make lot s and lots of antibodies
Then the bacterial all die and memery cells are born and u are all better after initating healing. finishthis