Category:Lymph Nodes

Anatomy & Physiology

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Lymph node responses in disease (The Total Node Response)

reactive nodes

• immunological response to antigens
• hyperplasia
• cell proliferation in cortex

- germinal centre activity

- multiplication of cells in thymus-dependent area (paracortex)

• accumulation of newly-formed plasma cells in medullary cords
• macroscopically

- bulging white cortex which may almost obliterate the medulla

lymphadenitis

• true inflammation
• swollen due to

- congestion

- oedema

- leukocyte (neutrophil) accumulation

• pyogenic organisms

- abscessation can develop

- there will be pus and necrosis in the node itself

• lymphangitis: inflammation of lymphatics

Role of the Lymph Node in Inflammation

Back to Inflammation - Pathology

• Antigenic material is transported in phagocytes via the tissue lymphatics to the local lymph node.
• In the subcapsular sinusoids of the lymph node, antigens are exposed to the reticular cell macrophages.
  • These macrophages form a meshwork around the subcapsular, cortical and medullary sinusoids.
  • These reticular cells present the antigen to the appropriate lymphocyte population.
    • To B-cells in the follicular centres
    • To T-cells in the parafollicular areas.
• When stimulated by antigen presentation, the respective areas undergo an increase in size by hperplasia.
  • The lymphocytes produced later leave the lymph node to seek out the source of the antigen in the damaged portion.
• Bacteria surviving the initial local inflammatory reaction also travel to the lymph node.
  • Travel either in macrophages or as a bacteraemia/septicaemia.
  • In the lymph node, many bacteria are trapped, degraded and killed, or exposed to antibody produced by plasma cells in the medullary area.
  • Bacteria set up an acute inflammatory response in the lymph node.
    • If they are pyogenic, baceria can produce abscessation in the lymph node.
      • E. g. Strangles.
        • An upper respiratory tract pathogen in the horse.
        • Abscesses in the cervical lymph nodes burst to the exterior.
        • Abscesses in the retropharyngeal node burst into the pharynx
        • Infection is usually localised to the head and neck, but can spread to cause abscessation elsewhere in the body.

Bacteraemia

• Bacteria may continue through the lymph nodes and circulate in the blood.
• These are generally cleared from the blood by other organs containing phagocytes.
  • E.g. the liver, spleen and lungs.
• There are species differences in the ability to remove bacteria.
  • In most species, the majority of clearance is carried out by the liver and spleen.
  • However, in the pig, the lung removes 60-80% of such bacteria.

Septicaemia

• Septicaemia is a condition where there are highly pathogenic bacteria circulating and rapidly multiplying in the blood.
  • Accompanied by severe signs of clinical illness due to the liberation of bacterial toxins.
    • High fever
    • Rapid respiration
    • Shock
  • Can result in the death of the animal.

Gross Appearance

• The lymph nodes, liver and spleen are very hyperaemic and swollen.

Histological Appearance

• Capillaries in tissues taken immediately after death show bacteria in their lumens.

Diseases Involving Reactive Nodes

Parasitic Diseases

bovine parasitic bronchitis

ostertagiasis

fascioliasis

Bacterial Diseases

clostridial

Diseases Involving Both Reactive Nodes and Lymphadenitis

Tuberculosis - Cattle

viz. brucellosis and Johne's disease

• chronicity is caused by persistence of intacellular bacteria in lymph node macrophages
• Type IV hypersensitivity, but does not result in visible necrosis as in TB

Johne's disease

Actinobacillosis

Actinomycosis

Equine strangles

• acute inflammation
• produce pyogenic or necrotic foci in the drainage nodes
• involves submaxillary nodes

Streptococcal adenitis or head gland disease

• dogs
• acute inflammation as in above

Diseases Parasitising the Lymphocytes

• organism grows in the lymphocytes and ruptures them
• if large infecting dose

- may be rapidly fatal since animal may no tb e able to mount an immunological attack

• if smaller infecting dose

- loss of mature lymphocytes causes a dramatic stimulation of the remaining lymphocyte precursors

- node hyperplasia follows

- competition between lymphocytolysis by the organism and lymphocyte production by the nodes

- clinically

- may be swelling of the node at one stage and reduction in size at another

canine distemper

• virus

swine fever

• virus

bovine east coast fever

• protozoan

Leishmaniasis in the dog

Other Lymphadenopathy

Lymph node pigmentation

• Lungs

- anthracosis

- carbon derived from soot finds its way to the local nodes in macrophages

• Skin

- dermatopathic lymphadenopathy or melanic reticulosis

- in pigmented animals, especially black dogs

- chronic inflammatory skin conditions lead to melanin deposition in hyperplastic nodules

- also occurs in nodes draining skin melanomas where the pigment may be the result of skin ulceration or secondary tumour deposit

- these two should not be confused since the prognosis is very different following surgery

Emphysema

• interstitial emphysema

- common in cases of dyspnoea

- more commonly affects bovine lung

- due to well developed pulmonary lobulation and hence much loose interstitial lung tissue

• collection of gas bubbles in bronchial and mediastinal lymph nodes

- gas travels to these nodes after gaining entry to the many lymphatic vessels present in the interstitial tissue

Neoplasia

• Primary tumours
  • Lymphosarcoma (lymphoma)

- of lymphoid cells with lymph node enlargement

- smooth, pale hemogenous but may have areas of necrosis

- may cause pseudo-hyperparathyroidism

• Secondary tumours

- nodes often involved in the spread of tumours by extension or metastasis

- usually carcinomas

Haemal Lymph Nodes

• ruminants only
• small; dark red/brown
• develop during foetal life

- lymph node primordia which lose their lymph vessles

- receive all cells and antigen from the BLOOD

• functional significance unclear
• probably respond to blood-borne antigen