Carrageenan works via the Bcl10, NF-κB, IκBα pathway to activate inflammation mediators.  This pathway initially involves phosphorylation steps followed by nuclear translocation of phospho-NF-κB. This sets off transcription and translation of inflammatory biomarkers such as COX, NOS, IL-6 etc. Inflammation causes many effects. One of the effects is vasodilation of capillaries/blood vessels.  Below the surface where carrageenan has been applied, inflammation thus cause dilation of the capillaries underneath the skin surface. Thus increased blood flow to the area. Manifest as swelling/redness of the affected area.

many mediators can be involved in carrageenan induced inflammtion such as Kinins, histamin and the prostaglandine, and carrageenan is capable of releasing kinin- like sucstances from plasma

Carrageenan is a complex polysaccharide that binds to TLR4, activating Bcl10 and the NFKB pathway. It is used to induce inflammation for the evaluating agents that might have anti-inflammatory properties. See the attached reference for mechanistic study and the reference below for use in models of inflammation.

Duarte DB, Vasko MR, Fehrenbacher JC. (2012) Models of Inflammation: carrageenan air pouch. Current Protocols in Pharmacology, Chapter 5

in line with answers above, please refer the attached paper

The mechanism responsible for carrageenan-induced immune suppression is believed to be its selective cytopathic effect on macrophages. This property of carrageenan has led to its adoption as a tool for analysing the role of these cells in the induction and expression of immune reactivity. Systemic administration of earrageenan may, however, induce disseminated intravascular coagulation and inflict damage on both the liver and kidney. This is an important consideration in the interpretation of the effects of carrageenan in vivo and precludes its use as a clinical immune suppressant.

I wonder if carrageenan might be related somehow to the Sannarelli-Shwartzman phenomenon?

Several previous studies that used carrageenan as an inflammatory irritant. The inflammatory mechanisms describes like this.  First carrageenan stimulates release of TNF-α which further induces IL-1β and IL-6, then stimulates the production of cyclooxygenase (COX) products and induces other cytokines, IL-8 thus stimulating local production of symphatic amines. Thus cascade cytokine release precedes the release of cyclooxidase (COX) and sympathomimetic amine product (Necas and Bartosikova, 2013) 

Thank you all for detailed answers

Hi,

In order to understand the inflammatory mechanisms caused by carrageenan you can check this paper : https://www.researchgate.net/publication/301550110_In_vitro_immunomodulatory_activity_and_in_vivo_anti-inflammatory_and_analgesic_potential_with_gastroprotective_effect_of_the_Mediterranean_red_alga_Laurencia_obtusa

Thank you sirine