Autoimmune Diseases
These are a group of disease where antibodies  (or CMI) are produced against self antigens, causing disease process.

Normally one's immune competent cells do not react against one's own tissues. This is due to self tolerance acquired during embryogenesis. Any antigen encountered at that stage is recognized as self and the clone of cells capable of forming the corresponding antibody is suppressed.

Mechanism of autoimmunity

(1) Alteration of antigen

-Physicochemical denaturation by UV light, drugs etc. e.g. SLE.
- Native protein may turn antigenic  when a foreign hapten combines with it, e.g. Haemolytic anemia with Alpha methyl dopa.

(2) Cross reaction: Antibody produced against foreign antigen may cross react with native protein because of partial similarity e.g. Rheumatic fever.

(3) Exposure of sequestered antigens: Antigens not normally exposed to immune competent cells are not accepted as self as tolerance has not been developed to them. e.g. thyroglobulin, lens protein, sperms.

(4) Breakdown of tolerance : 
Emergence of forbidden clones (due to neoplasia of immune system as in lymphomas and lymphocytic leukaemia)
Loss of suppressor T cells as in old age and CMI defects

Autoimmunity may be
Organ specific.
Non organ specific (multisystemic)

I. Organ specific

(1) Hemolytic anaemia:

Warm or cold antibodies (active at 37° C or at colder temperature)
They may lyse the RBC by complement activation or coat them and make them vulnerable to phagocytosis

(2) Hashimoto's thyroiditis:
 
Antibodies to thyroglobulin and microsomal antigens.
Cell mediated immunity.
Leads to chronic. destructive thyroiditis.

(3) Pernicious anemia

Antibodies to gastric parietal cells and to intrinsic factor.

2. Non organ specific.

Lesions are seen in more than one system but principally affect blood vessels and
connective tissue (collagen diseases).

1. Systemic lupus erythematosus  (SLE). Antibodies to varied antigens are seen. Hence it is possible that there is abnormal reactivity of the immune system in self recognition.

Antibodies have been demonstrated against:

Nuclear material (antinuclear I antibodies) including DNA. nucleoprotein etc. Anti nuclear antibodies are demonstrated by LE cell test.
Cytoplasmic organelles- mitochondria, rib osomes, Iysosomes.
Blood constituents like RBC, WBC. platelets, coagulation factors.

Mechanism. Immune complexes of body proteins and auto antibodies deposit in various
organs and cause damage as in type III hypersensitivity

Organs involved
Skin- basal dissolution and collagen degeneration with fibrinoid vasculitis.
Heart- pancarditis.
Kidneys- glomerulonephritis of focal, diffuse or membranous type 
Joints- arthritis. 
Spleen- perisplenitis and vascular thickening (onion skin).
Lymph nodes- focal necrosis and follicular hyperplasia.
Vasculitis in other organs like liver, central or peripheral nervous system etc,

2. Polyarteritis nodosa. Remittant .disseminated necrotising vasculitis of small and medium sized arteries

Mechanism :- Not definitely known. Proposed immune reaction to exogenous or auto antigens 

Lesion : Focal panarteritis- a segment of vessel is involved. There is fibrinoid necrosis
with initially acute and later chronic inflammatory cells. This may result in haemorrhage
and aneurysm.

Organs involved. No organ or tissue is exempt but commonly involved organs are :
- Kidneys.
- Heart.
- Spleen.
- GIT

3. Rheumatoid arthritis. A disease primarily of females in young adult life. 

Antibodies
- Rheumatoid factor (An IgM antibody to self IgG)
- Antinuclear antibodies in 20% patients.

Lesions

- Arthritis which may progress on to a crippling deformity.
- Arteritis in various organs- heart, GIT, muscles.
- Pleuritis and fibrosing alveolitis.
- Amyloidosis is an important complication.

4. Sjogren's  Syndrome. This is constituted by 

- Kerato conjunctivitis sicca
-Xerostomia
-Rheumatoid arthritis. 

Antibodies

- Rheumatoid factor
- Antinuclear factors (70%).
- Other antibodies like antithyroid, complement fixing Ab etc
- Functional defects in lymphocytes. There is a higher incidence of lymphoma

5. Scleroderma (Progressive systemic sclerosis)
Inflammation and progressive sclerosis of connective tissue of skin and viscera.

Antibodies

- Antinuclear antibodies.
- Rheumatoid factor. .
- Defect is cell mediated.

lesions

Skin- depigmentation, sclerotic atrophy followed by cakinosis-claw fingers and mask face.
Joints-synovitis with fibrosis
Muscles- myositis.
GIT- diffuse fibrous replacement of muscularis resulting in hypomotility and malabsorption
Kidneys changes as in SLE and necrotising vasculitis.
Lungs – fibrosing alveolitis.
Vasculitis in any organ or tissue.

6.Wegener’s granulomatosis. A complex of:
Necrotising lesions in upper respiratory tract.
Disseminated necrotising vasculitis.
Focal or diffuse glomerulitis.

Mechanism. Not known. It is classed with  autoimmune diseases because of the vasculitis  resembling other immune based disorders.
 

Pleural effusion is a medical condition where fluid accumulates in the pleural cavity which surrounds the lungs, making it hard to breathe.

Four main types of fluids can accumulate in the pleural space:

Serous fluid (hydrothorax)

Blood (hemothorax)

Lipid (chylothorax)

Pus (pyothorax or empyema)

Causes:

Pleural effusion can result from reasons such as:

• Cancer, including lung cancer or breast cancer
• Infection such as pneumonia or tuberculosis
• Autoimmune disease such as lupus erythematosus
• Heart failure
• Bleeding, often due to chest trauma (hemothorax)
• Low oncotic pressure of the blood plasma
• lymphatic obstruction
• Accidental infusion of fluids

Congestive heart failure, bacterial pneumonia and lung cancer constitute the vast majority of causes in the developed countries, although tuberculosis is a common cause in the developing world.

Diagnosis:

1. Gram stain and culture - identifies bacterial infections
2. Cell count and differential - differentiates exudative from transudative effusions
3. Cytology - identifies cancer cells, may also identify some infective organisms
4. Chemical composition including protein, lactate dehydrogenase, amylase, pH and glucose - differentiates exudative from transudative effusions
5. Other tests as suggested by the clinical situation - lipids, fungal culture, viral culture, specific immunoglobulins

Keloids
1. Characterized by a progressively enlarging scar.
2. Caused by an abnormal accumulation of collagen at the site of injury.
3. More common in African-Americans.

Peutz-Jeghers syndrome
1. Lesions appear as small, melanotic, and freckle-like. They can be found on the skin, oral mucosa, lips, feet, and hands. 
2. May also present with intestinal polyps, which may develop into a gastrointestinal carcinoma. 
3. Genetic transmission: autosomal dominant.

Pulmonary Hypertension 

Sustained elevation of mean pulmonary arterial pressure.

Pathogenesis 
Elevated pressure, through endothelial cell dysfunction, produces structural changes in the pulmonary vasculature. These changes ultimately decrease pulmonary blood flow and stress the heart to the point of failure. Based on etiology, pulmonary hypertension is divided into two categories.

Primary (idiopathic): The cause is unknown.
Secondary: The hypertension is secondary to a variety of conditions which increase pulmonary blood flow or increase resistance to blood flow. Example: Interstitial fibrosis.
Pathology 
The changes involve large and small pulmonary blood vessels and range from mild to severe. The major changes include atherosclerosis, striking medial hypertrophy and intimal fibrosis of small arteries and arterioles, and plexogenic arteriopathy. Refer to Figure 15-7 in your textbook.

Pathophysiology 
Dyspnea and fatigue eventually give way to irreversible respiratory insufficiency, cyanosis and cor pulmonale.

Blastomycosis (North American Blastomycosis; Gilchrist's Disease)

A disease caused by inhalation of mold conidia (spores) of Blastomyces dermatitidis, which convert to yeasts and invade the lungs, occasionally spreading hematogenously to the skin or focal sites in other tissues.

Pulmonary blastomycosis tends to occur as individual cases of progressive infection

Symptoms are nonspecific and may include a productive or dry hacking cough, chest pain, dyspnea, fever, chills, and drenching sweats. Pleural effusion occurs occasionally. Some patients have rapidly progressive infections, and adult respiratory distress syndrome may develop.