APECED

autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy

• development of thymocytes in the thymus gland • stochastic process -T-cell antigen receptors that

can bind to self antigens • negative selection • bone marrow derived dendritic cells and

macrophages; thymic epithelial cell• ???myriad of self antigens, many of them organ

specific, get to the thymus gland to be “seen” by developing thymocytes???

In mice transgenic for a TCR that recognizes a known peptide antigen complexed with self MHC, all the T cells have the same specificity. In the absence of the peptide, most thymocytes mature and emigrate in the periphery. This can be seen in the bottom left panel, where a normal thymus is stained with antibody to identify the medulla (in green) and by the TUNEL technique to identify apoptotic cells (in red). If the mice are injected with the peptide that is recognized by transgenic T cell receptor, then massive cell death occurs in the thymus, as shown by increased numbers of apoptotic cells in the right hand bottom panel.

Bone marrow derived cells mediate negative selection in the thymus: When MHCaxb F1 bone marrow is injected into an irradiated MHCamouse, the T cells mature on thymic epithelium expressing only MHCa molecules.Nevertheless, the chimeric mice are tolerant to skin grafts expressing MHCb molecules (provided that these grafts do not present skin-specific peptides that differ between strains a and b). This implies that the T cells whose receptors recognize self antigens presented by MHCb have been eliminated in the thymus. As the transplanted MHCaxb F1 bone marrow cells are the only source of MHCb molecules in the thymus, bone marrow derived cells must be able to induce negative selection.

• RJ, male, 18 months• Dry skin, sluggish movements.• Pediatrician’s diagnosis: hypothyroidism - thyroid hormone

(Synthyroid) - a few weeks - much improved.• By the time the child was almost 6 years old, his mother felt he was

not growing at normal rate. The pediatrician referred the child to an endocrinologist. – height and weight were below the third centile for his age. – X-ray wrist: bone age of 3years/6 months (5years/10 months)

• Blood test: thyroid stimulating hormone (TSH) was >60 ng/dl-1 (several times the upper limit of normal TSH levels) - inadequate thyroid hormone replacement. The dose of Synthroid was increased from 0.05 to 0.075 mg/day.

• The child resumed his normal growth and his bone age subsequently caught up with his actual age.

• sister, 2 years older• - hypoparathyroidism, • - serum antibodies against islets of the pancreas (but no

clinically apparent diabetes) and • - Grave’s disease (autoimmune hypoparatiroidism). Suspicion of inherited disease APECED - autosomal

recessively inherited abnormality. The serum calcium levels were tested to make sure that he

had not developed hypoparathyroidism like his sister, but they were normal.

No antibodies against any other endocrine glands were found either.

• The patient’s fingernails: thickened, longitudinal notches and ridging.

• Referred to a dermatologist - consistent to autoimmune polyglandular syndrome.

• Nail scrapings cultured for Candida albicans: negative.

• Two patches of hair loss at the top and back of the scalp.

• Easily pull out the hair, whose roots looked atrophied under the microscope: alopecia areata (patchy hair loss).

Abnormal growth (dysplasia) of fingernails in APECED

• The patient continued to grow satisfactory• 8 years old: TSH level was 2.5 ng/dl-1 (normal) -

adequate thyroid hormone replacement. • Continued to lose hair in patches• Lost his eyebrows. • Developed fissures at the angle of his mouth - infection

with C. albicans. • He was taunted at school about his bizarre appearance

and his schoolwork deteriorated. • With his parent’s divorce pending, he became

depressive and took an overdose of Synthroid in a suicide attempt.

• He received intensive psychotherapy for his depression.

• Puberty: scrotum and areolae around his nipples became darkly pigmented

• Suspicion of adrenal insufficiency (Addison’s disease).

• Blood test: adrenocorticotropic hormone (ACTH) three times the upper limit of normal.

• Steroid prednisone at 5 mg/day and Fluorinef (which conserves sodium and potassium excretion) at 0.1 mg/day.

• 18 years old - he noticed that he had started to bruise easily and that his gums bled after brushing his teeth.

• Hematology: low platelet count of 34,000/mm3.

• Diagnosis of idiopathic thrombocytopenic purpura (ITP).

• APECED also known as autoimmune poliglandular syndrome (APS) type 1.

• several polyglandular disease of unknown origin• APECED - the only one to have a pattern of autosomal recessive

inheritance. • wide range of autoantibodies against:• - organ-specific antigens of the endocrine glands,• - antigens in the liver and skin,• - blood cells such as platelets. • Abnormalities of various ectodermal elements:• -fingernail, • - teeth• - skin. • Increased susceptibility to infection with the yeast Candida albicans.

• High incidence among Finns, Sardinians and Iranian Jews, as high as one in 9,000 births in some populations.

• This made it possible to map the gene responsible to chromosome 21 in affected Finnish families. The gene was cloned and named AIRE (autoimmune regulator).

• It was the first identified gene outside the MHC to be associated with autoimmune disease, and seems to encode a transcriptional regulator. T

• The two brothers were found to have a deletion of 13 base pairs in exon 8 of the gene. Their parents were both heterozygous for this mutation.

• When the equivalent gene aire was knocked out in mice by homologous recombination - autoimmune disease just like the human patients;

• Extent and severity of these autoimmune diseases progressed as the mice aged.

• The protein AIRE - normally expressed predominantly - thymic medullar epithelial cells; weakly in peripheral lymphoid tissue.

• AIRE was found to act as transcriptional activator in the thymus, where it induces the expression of 200-1200 genes, including genes that encode organ-specific antigens of the salivary glands and the zona pellucida of ova among others.

• Expression of self antigens - negative selection • When AIRE is lacking, these antigens are also not present - the potentially

self-reactive T cells are not removed from the repertoire in the thymus and leave to cause autoimmune reactions in peripheral organs.

• It is not clear yet how deficiency of AIRE causes ectodermal abnormalities and susceptibility to candidiasis.

Ovarian follicles stained with serum from patient with APECED (AIRE -/-). Serum was reacted with a microscopic section of ovary and then with fluorescent antibody against human IgG.

It seems paradoxical that the patient developed hypoparatiroidism while his sister had hyperthyroidism (Grave’s disease). How can this be explained?

• Grave’s disease - autoantibodies against the receptor for TSH in the thyroid gland - act as agonist (like TSH) - stimulates the thyroid to become hyperactive.

• This patient - thyroid gland gradually destroyed by the infiltration of cytotoxic T cells specific for a thyroid antiogen - Hashimoto’s disease.

• *He could possibly also have developed an anti-TSH antibody that antagonized TSH. In fact, patients with Grave’s disease can sometimes go on to develop Hashimoto’s disease, and both stimulatory and blocking autoantibodies can be present in both diseases.

Feed-back regulation of thyroid hormone production is disrupted in Grave’s disease. Grave’s disease is caused by autoantibodies specific for the receptor for thyroid stimulating hormone (TSH). Normally, thyroid hormones are produced in response to TSH and limit their own production by inhibiting the production of TSH by the pituitary gland (left panels). In Grave’s disease, the autoantibodies are agonists for the TSH receptor and therefore stimulate the production of thyroid hormones (right panels). The thyroid hormones inhibit TSH production in the normal way but do not affect production of the autoantibody; the excessive thyroid hormone production induced in this way causes hyperparathyroidism

What caused the deep pigmentation of the scrotum and the areolae around the nipples that led to the suspicion that he had developed an autoantibody against his adrenal cortical cells (Addison’s disease)?

• The loss of adrenal cortical hormones as a result of the autoimmune destruction of his adrenal cortex caused patient’s pituitary gland to secrete greatly increased amounts of ACTH. ACTH is composed of 39 aa, the amino-terminal 14 aa of which can be cleaved off by trypsin-like enzymes. This 14 amino-acid peptide is called melanocortin and stimulates melanocytes in the skin to produce brown pigment melanin. The receptor for melanocortin also binds intact ACTH, albeit at a lower affinity. The increased amounts of ACTH, and probably of melanocortin, were what led to the increased pigmentation of the scrotum and tissue around his nipples.

What abnormality might be found in the lymph nodes of the mice that lacked the aire gene?

• They had twice the normal number of CD4+ and CD8+ effector/memory cells in their lymph nodes. This apparently resulted from a lack of negative selection of autoreactive cells in the thymus.

• Sluggish movements & dry skin

• Growth delay

• Brothers/sisters with various congenital autoimmunities (possibly different)

• Genetic confirmation

• Worsening due to the development of new autoimmune manifestations