On chromosome 6 of the human genome, there is a major histocompatibility complex called human leukocyte antigen.
Size: about 3.6 Mb
Telomeric class 1, centromeric class 2, and class 3 region make up the three classes.
Since humans are highly polymorphic, different alleles can be found in a population's various members. With the exception of identical twins, no two people can have the same kind of MHC molecules.

MHC Molecule History

Murine MHC locus H2 was discovered by George Snell.
Dausset discovered HLA on the human chromosome's WBC.
The importance of these molecules in the immune response was noted by Baruj Benacerraf.
In 1980, they shared the medical Nobel Prize with three other people.

MHC Molecule Functions

Antigen presentation—the fundamental job of the MHC molecule—involves breaking down the foreign peptide and presenting it to T lymphocytes. This enables T cells to identify the foreign antigen with more specificity and produce antibodies against it, neutralizing it.

Difference between MHC class I and MHC class II molecules

MHC class I	MHC class II
Present on the surface of all nucleated cells	Present on antigen-presenting cells
Present antigen to CD8+ cells (cytotoxic T lymphocytes)	Present antigen to CD4+ cells (T helper cells)
Bind to endogenous antigen	Bind to exogenous antigen

Process of thymic selection

Weak connections with self-peptide-MHC allow T cells to survive (positive selection), but strong contacts result in death. This is how thymic selection primarily relies on the detection of self-peptide-MHC complexes (negative selection).

What is Autoimmunity?

Loss of the cell's capacity to distinguish between self and non-self leads to autoimmune diseases.
Antigen presentation is the mechanism by which the T-cell receptor, which is present in the antigen-presenting cell (APC), identifies the digested peptide fragment of the antigen that is delivered by the MHC molecule.
Pure thymic selection of self-peptide-MHC complex and non-self-peptide-MHC complex, a crucial selection process that occurs in the thymus during T-cell maturation, is the cause of the inability to distinguish between self and non-self.

The MHC Molecule And Autoimmunity - Examples And Diagrams by Doctor-Dr

Association of MHC with the autoimmune disorder

It is not entirely clear how MHC and autoimmune disorders are related.
The predominant theory up to this point is that it results from a failure in immunological tolerance, or the cell's capacity to distinguish between self and nonself antigenic peptides.
The loss of cell selection in the thymus is the cause of several illnesses, such as type I diabetes (TID), multiple sclerosis, rheumatoid arthritis, graves' disease, ankylosing spondylitis, systemic lupus erythematosus, etc.

Examples of autoimmune disorders

1. Multiple Sclerosis:

It is an inflammatory demyelinating condition that is persistent.
Central nervous system effects
It is challenging for the brain to transmit messages to the body when the myelin sheath, a covering of nerve cells, is attacked by activated T cells and macrophages at the central nervous system (CNS), where they penetrate the blood-brain barrier.

The symptoms might vary from person to person.
Hands, legs, and other parts of the body that are on one side of the body are numb or weak, and you may experience electric shock-like feelings while bending your neck.
Ineffective coordination
not being able to walk correctly
hazy vision
Although interim treatments can be used to address symptoms, there is no permanent cure.

2. Rheumatoid Arthritis:

chronic systemic autoimmune disorder
affects the lining of synovial joints
associated with progressive disability, premature death, and socioeconomic burdens
mainly females than males, and mainly observed in elderly people.

Symptoms:
Arthralgia (pain in joints)
Swelling and redness in joints
Limiting joint motion
Weight loss
Fever
fatigue
No permanent cure, but temporary treatment can help to treat symptoms
Breastfeeding can decrease the rate of occurrence of RA in females.

3. Type 1 Diabetes:

autoimmune condition caused by T cells.
Insulin shortage brought on by the loss of pancreatic beta-cells results in hyperglycemia and a propensity for ketoacidosis.
Although the condition can manifest at any age, it frequently manifests in childhood or adolescent.
Only 5–10% of patients with diabetes have T1D; the remainder have type 2, monogenic types of diabetes, or diabetes brought on by other causes of islet cell damage.
Because insulin helps sugar enter the bloodstream, when autoimmune cells attack the pancreatic beta cells, which are responsible for producing insulin, sugar builds up in the body and raises blood sugar levels.
Islet-cell autoantibodies, autoantibodies against insulin, glutamic acid decarboxylase (GAD), or tyrosine phosphates IA-2 and IA-2β, and ZnT8 are antibody indicators of autoimmune against β-cell.
Human leukocyte antigen (HLA) genes DQA and DQB have been linked in studies to illness risk.

Symptoms:
weightloss
Frequent urination
Impaired vision
Hunger attacks

4. Systemic Lupus Erythematosus:

autoimmune systemic illness accompanied with multiorgan inflammation
Loss of self-tolerance results from autoimmune antibodies' formation of nucleic acid and the proteins that bind to it again.
The production of inflammatory cytokines, which induce tissue damage, and the activation of autoreactive B and T cells, which cause organ damage, are both significantly influenced by innate immunity.
Symptoms:
fever
skin rashes
pain or swelling in joints
sun sensitivity
oral ulcers
heart, kidney, lungs problems
psychosis

5. Psoriasis

Chronic inflammatory skin disease
Show comorbidity with another autoimmune disease such as arthritis.

Symptoms:
Scaly red patches confined to a specific area
Nails with thick pitted or ridged lining
Stiff and swollen joints
Bleeding in skin due to extreme dryness
Itching
Burning
Painful lesions
Since this disease's symptoms appear erratically and can occasionally lay latent in the body for years, there is no permanent cure. However, a few drugs can help alleviate symptoms, such as the immunosuppressant methotrexate.

6. Dermatomytosis

the body's inability to distinguish its own cells as alien, a hereditary factor, cancer in elderly individuals, an infection, a drug, etc.
Rashes and muscular irritation are the results.
Symptoms:
Painful sunburn rashes
Upper eyelid swelling
Spots of red and purple color on knee, elbow, toes, and knuckles
Stiffness and pain in joints
Hair thinning with dry skin
Red fingernails
Weakness in muscles around the hip, back, shoulder, and neck
Weightloss
Tiredness
Blood tests, an electromyogram, an MRI, a biopsy of the skin or muscle, etc. can all be used to make a diagnosis.
Immunosuppressive medications, including tacrolimus, methotrexate, and azathioprine, are used throughout treatment.

7. Celiac Disease

Also known as gluten-sensitive enteropathy, nontropical sprue, and celiac sprue.
a long-term autoimmune digestive condition that affects the small intestine and is brought on by consuming gluten, which is naturally present in grains like wheat and barley.
About 1% of the world's population has this condition.
Symptoms:
Bloating
Chronic diarrhea
Constipation
Gas
Lactose intolerance
Nausea and vomiting
Pain in abdomen
Genetic testing and biopsies of the small intestine are usually done for diagnosis
No permanent cure

8. Inflammatory Bowel Disease: Ulcerative Colitis and Crohn’s Disease

Two disorders, namely Crohn's disease and ulcerative colitis, are characterised by chronic gastrointestinal tract inflammation.
Affected areas of the small intestine are typically affected by Chrohn's disease, which manifests as patches of damage in any portion of the GI tract. All layers of the GI tract are impacted by the inflammation.
Ulcerative colitis doesn't manifest in patches and affects the big intestine and rectum. only impact the big intestine's innermost layer.

Symptoms:
Persistent diarrhea
Abdominal pain
Rectal bleeding/bloody stools
Weight loss
Fatigue
The diagnosis was done by endoscopy and colonoscopy.

The MHC Molecule And Autoimmunity - Examples And Diagrams by Doctor-Dr