Following attachment of H. pylori to stomach epithelial cells, the type IV secretion system expressed by the cag PAI "injects" the inflammation-inducing agent, peptidoglycan, from their own cell walls into the epithelial cells. The injected peptidoglycan is recognized by the cytoplasmic pattern recognition receptor (immune sensor) Nod1, which then stimulates expression of cytokines that promote inflammation.The type-IV secretion apparatus also injects the cag PAI-encoded protein CagA into the stomachs epithelial cells, where it disrupts the cytoskeleton, adherence to adjacent cells, intracellular signaling, cell polarity, and other cellular activities. Once inside the cell, the CagA protein is phosphorylated on tyrosine residues by a host cell membrane-associated tyrosine kinase (TK). CagA then allosterically activates protein tyrosine phosphatase/protooncogene Shp2. Pathogenic strains of H. pylori have been shown to activate the epidermal growth factor receptor (EGFR), a membrane protein with a TK domain. Activation of the EGFR by H. pylori is associated with altered signal transduction and gene expression in host epithelial cells that may contribute to pathogenesis. A C-terminal region of the CagA protein (amino acids 873–1002) has also been suggested to be able to regulate host cell gene transcription, independent of protein tyrosine phosphorylation. A great deal of diversity exists between strains of H. pylori, and the strain that infects a person can predict the outcome. Cancer
Two related mechanisms by which H. pylori could promote cancer are under investigation. One mechanism involves the enhanced production of free radicals near H. pylori and an increased rate of host cell mutation.
Chorioangioma, or chorangioma, is a benign tumor of placenta. It is a hamartoma-like growth in the placenta consisting of blood vessels, and is seen in approximately 0.5 to 1% pregnancies. It is mostly diagnosed ultrasonically in the second trimester of pregnancy. Large chorioangiomas are known to cause complications in pregnancy, while the smaller ones are asymptomatic. Presentation
Most chorangiomas are not clinically significant, i.e. they do not have an adverse effect on placental function. Complications
Large (greater than 4 or 5 cm.) or multiple chorioangiomas may lead to complication. The complications are polyhydramnios, preterm labour, hemolytic anemia, fetal cardiomegaly, fetal thrombocytopenia, intrauterine growth retardation, preeclampsia, abruption of placenta and congenital anomalies. Pathogenesis
The origin of chorioangioma is from primitive chorionic mesenchyme. It develops when the blood vessels and stroma undergo rapid proliferation independent of the surrounding tissue. Based on histological features, chorioangioma is classified by Marchetti into three types:
Cellular type : This type is immature and contains mostly cellular elements packed compactly. Angiomatous (vascular) type : This is the most common type of choriocarcinoma. It is distinguished by the presence of numerous small blood vessels. Degenerative type : This is the mature type with degenerative changes.Each type is believed to represent a phase of tumor development. Chorioangioma has no malignant potential. Diagnosis
Most chorioangiomas are asymptomatic. They are generally picked up in second trimester scan. Chorioangioma is seen as a hypo- or hyperechoic circumscribed mass that is distinct from the placenta at gray-scale US examination. Large lesions may contain fibrous septa.