Children with H. pylori-related gastritis showed the following: (1) increased MMP-2 and TIMP-2 plasma levels, (2) increased intracellular expression of MMP-2 in the circulating lymphocytes and neutrophils, (3) low frequencies of circulating TIMP-1+ and TIMP-2+ leukocytes, and (4) high expression of mRNA for MMP-9 along with low expression of mRNA for MMP-2 in the gastric mucosa. This evidence concerns the gene MMP9 and gastritis.