Clinical correlate - Thoracic duct: The thoracic duct can be ruptured during surgery in the neck or thorax. This may present as a fistula that leaks chyle (a milky white fluid). Chylothorax is the accumulation of chyle in the pleural space. It can occur after penetrating chest injuries or thoracic surgery, and it may also be associated with lymphomas, cirrhosis, filariasis, sarcoidosis, tuberculosis, amyloidosis, and (rarely) congenital causes. Clinically, it presents as a pleural effusion.
Lymphocyte homing: Think of this as “coming home.” After activation by pathogens, T cells and B cells travel to lymph nodes. The chemokines CCL19 and CCL21 are essential for lymphocyte transmigration across high endothelial venules (HEVs). HEVs are specialized postcapillary venules found in lymph nodes and Peyer’s patches. CCL21 is constitutively expressed within the lumen of HEVs, while CCL19 is produced by other cells within the lymph node. CCL19 and CCL21 are ligands for the chemokine receptor CCR7. CCR7 is expressed by HEVs, T cells, B cells, and dendritic cells.
Splenomegaly causes: The most common causes of splenomegaly include:
Liver disease (cirrhosis, hepatitis)
Acute or chronic infection (bacterial endocarditis, infectious mononucleosis, HIV, malaria, tuberculosis, histiocytosis)
Hematologic malignancy (lymphomas, leukemias, myeloproliferative disorders)
Congestion (splenic vein thrombosis, portal hypertension, congestive heart failure)
Inflammation (sarcoidosis, lupus, rheumatoid arthritis, systemic lupus)
Splenic sequestration (pediatric sickle cell, hemolytic anemias, thalassemias)
Other (metastases, abscess, trauma, hemangiomas, rare drug reactions (RhoGam), cysts, Gaucher Disease, Niemann-Pick disease)
Differences between chyle and lymph: Chyle is a milky, opalescent fluid that contains chylomicrons and very low-density lipoproteins (formed from dietary long-chain triglycerides), along with cells. Chyle is rich in protein, fat, and white blood cells. Prolonged, high-volume loss of chyle can lead to nutritional failure and immunosuppression. Lymph is similar to plasma and interstitial fluid and consists mainly of proteins and immune cells. Lymph from the GI tract is chyle because it contains fats absorbed from food.
M cells: Poliovirus, Reoviruses (think Rotavirus), EPEC E.coli, CXCR4 tropic strains of HIV, Shigella flexneri, Salmonella typhimurium, Yersinia pseudotuberculosis and Prions bind to M cells and penetrate the intestinal epithelium in this way.
MALToma: MALToma is a lymphoma (also called marginal zone B cell lymphoma) that arises from MALT tissues, most commonly in the stomach. It is of B cell origin and is associated with chronic gastritis caused by H pylori. In early stages, treatment of H.pylori infection can lead to complete resolution of the lymphoma. Other associations for MALTomas are - Chlamydia psittaci and ocular adnexal MALT lymphoma, Hepatitis C virus and salivary gland MALT lymphoma, and C. jejuni and immunoproliferative small intestinal disease.