In autoimmune gastritis , the immune system attacks the parietal cells leading to hypochlorhydria (low stomach acid secretion). This results in an elevated gastrin level in an attempt to compensate for increased pH in the stomach. Eventually, all the parietal cells are lost and achlorhydria results leading to a loss of negative feedback on gastrin secretion. Plasma gastrin concentration is elevated in virtually all individuals with mucolipidosis type IV (mean 1507 pg/mL; range 400-4100 pg/mL) (normal 0-200 pg/mL) secondary to a constitutive achlorhydria. This finding facilitates the diagnosis of patients with this neurogenetic disorder.  Additionally, elevated gastrin levels may be present in chronic gastritis resulting from H pylori infection. 
Secondary to acting on its receptor, HM74A, niacin induces release prostaglandin D2 (PGD 2 )  via β-Arrestin1  in epidermal cells known as Langerhans.   This effect occurs fairly rapidly following oral ingestion of 500mg of niacin in subjects who experience the flush, as assessed by serum levels of its metabolite 9α, 11β-PGF2.  As production of prostaglandins requires the activity of cyclooxygenase (COX) enzymes, production of prostaglandins from niacin can be partially reduced with COX inhibitors such as aspirin.   The receptor that PGD 2 acts upon (the DP 1 receptor) can also be blocked which is the mechanism of the pharmaceutical laropiprant,  commonly prescribed alongside niacin to improve adherence. 
Type VI secretion systems were originally identified in 2006 by the group of John Mekalanos at the Harvard Medical School (Boston, USA) in two bacterial pathogens, Vibrio cholerae and Pseudomonas aeruginosa .   These were identified when mutations in the Hcp and VrgG genes in Vibrio Cholerae led to decreased virulence and pathogenicity. Since then, Type VI secretion systems have been found in a quarter of all proteobacterial genomes, including animal, plant, human pathogens, as well as soil, environmental or marine bacteria.   While most of the early studies of Type VI secretion focused on its role in the pathogenesis of higher organisms, more recent studies suggested a broader physiological role in defense against simple eukaryotic predators and its role in inter-bacteria interactions.   The Type VI secretion system gene clusters contain from 15 to more than 20 genes, two of which, Hcp and VgrG, have been shown to be nearly universally secreted substrates of the system. Structural analysis of these and other proteins in this system bear a striking resemblance to the tail spike of the T4 phage, and the activity of the system is thought to functionally resemble phage infection.