Question

Alexa is a 25 year old graduate student who arranged an urgent appointment with her primary care provider because her ‘vision is blurry’ in her left eye. She states that two days ago her vision changed. She compares her visual field to looking through a fogged up window. Her provider interprets this to mean she has a decrease in contrast and brightness. Eye examination reveals a marked reduction of visual acuity of her left eye. A swinging flashlight test reveals an afferent pupillary defect (Marcus Gunn pupil) of her left eye (i.e., paradoxical papillary dilatation in response to increased light). Visual acuity and pupillary responses in her right eye are normal. Assessment of the retina and retinal vessels in both eyes is normal. Additional findings show patchy but consistent hypoesthesia (decreased feeling) to pin and light touch over her right limbs. On questioning, Alexia states that she experienced a self-limiting episode of numbness and tingling a few months ago. She also states that she has been experiencing fatigue, particularly at the end of the day. She denies depression, and her family history is unrevealing. The remainder of the physical exam in normal. Alexa is referred to an ophthalmologist who diagnoses optic neuritis (inflammation of the optic nerve). She begins corticosteroid treatment, and is referred to a neurologist who schedules a cranial MRI with gadolinium. The MRI reveals the presence of multiple deep white matter lesions scattered throughout the brain, suggesting multiple sclerosis. A subsequent lumbar puncture and analysis of Alexia’s cerebral spinal fluid (CSF) is consistent with possible multiple sclerosis. Further work-up rules out other possible causes. Ultimately, the neurologist diagnoses Alexia with relapsing-remitting multiple sclerosis.

1. Multiple sclerosis is an autoimmune disease, in which the immune system reacts to self-antigen (i.e., loss of self-tolerance). What is self-tolerance? Describe the processes (central and peripheral) that allow the immune system to develop self-tolerance, and how self-tolerance might be compromised.

Answer 1

Self-tolerance is the ability of the immune system to recognize self-produced antigens as a non-threat while appropriately mounting a response to foreign substances. This balance of immunological defense and self-tolerance is critical to normal physiological function and overall health. Tolerance to self is a normal state that is maintained chiefly by clonal deletion of developing T and B cells and clonal deletion or inactivation of mature peripheral T and B cells

As lymphocytes develop, the receptor sequences are generated completely at random. This indiscriminate approach results in such a diverse variety of receptors that nearly any antigen the immune system encounters may be recognized. this broad repertoire inevitably contains receptors that can recognize endogenous antigens, self-made molecules which the immune system should not attack. In order to reduce the scope of lymphocytes recognition and subsequent attack of foreign antigens, the immune system employs a series of checks known as "self-tolerance". Self-tolerance regulation of immune effector cells can be divided into two mechanisms ;

1 central tolerance

2.peripheral tolerance

depending on where they take place.

Central tolerance occurs in the organ of maturation for the respective lymphocyte, the thymus for T-Cells and bone marrow for B-Cells. Peripheral tolerance occurs outside the organ of maturation, at the site of antigen recognition where the T-Cells and B-Cells would ultimately begin to elicit an immune response. Specifically, this can occur in the circulation, lymph node, lymph organ, or other tissue