LOCAL HUMORAL AND CELULAR IMMUNE RESPONSE TO H. PYLORI IN CHILDREN

Abstract

66 Background: The importance of mucosal immune response to H. pylori (Hp) in the regulation and immunopathology of gastritis is still unclear, especially in early stages of infection. Previous studies in adults have shown a specific local antibody response (mainly IgA class), and suggested the involvement of a particular lymphocyte profile (CD4 and CD8 subsets predominance in lamina propria and epithelium, respectively). However, this issue has been insufficiently addressed in pediatric age, where it may be relevant, particularly in areas of high prevalence and early acquisition of infection. Aims: To evaluate quantitative humoral and celular mucosal immune response in children with Hp infection, their eventual association with histology scores and Cag A status. Methods: Hp status of 28 children referred for upper GI endoscopy was assessed according to conventional criteria (urease, culture, histology) and allocation to Hp+ve or-ve (control) group, based respectively on at least two positive tests or negativity of all tests (status Hp+ve n=15; mean age 9,3 yrs; Hp-ve n=13; mean age 8,0 yrs). Sera and biopsy specimens (antral/transitional) were maintained frozen at -70°C and specific antibodies determined by a in-house ELISA technique (sera dilution IgG, IgA: 1/100; biopsies dilution IgG: 1/10; IgA: 1/2). Additional biopsies (formalin-fixed) were stained for conventional histology (Sidney System) and immunohistochemistry (indirect immunoperoxidase technique), using monoclonal antibodies against T cells (CD3, CD4, CD8), B cells (CD20) and plasmocytes (IgG, IgA). Lymphocyte and plasmocyte subsets were counted at a ×1000 magnification, in lamina propria (calibrated graticule; results expressed in cells/mm2) and epithelium (CD4, CD8/100 epithelial cells). Serum Cag A status was determined using a W Blotting Assay (Helicoblot 2.0). Results: Concerning humoral immune response, mean OD (optical density) was higher in Hp+ve cases both for serum (mean Hp+ve IgG: 0,368; IgA 0,194, mean Hp-ve IgG: 0,192; IgA 0,128 and mucosal antibodies mean Hp+ve IgG: 0,52; IgA 0,228; mean Hp-ve IgG: 0,02; IgA 0,076), though with statistical significance (Mann-Whitney Test) only for serum (p<0,05) and mucosal (p<0,0001) IgG. Lamina propria lymphocyte counts showed a significant (p<0,01) increase of T cell subset (CD3+) in Hp+ve cases (mean +ve476,5; -ve344,8); plasmocyte counts (IgG, IgA) predominated in Hp+ve (mean Hp+ve IgG pl. 96,7; IgA pl. 570,4vs mean Hp-ve IgG pl. 41,9; IgA pl. 342,2); CD4 and CD8 subsets were not significantly different in Hp+ve vs -ve cases (lamina propria and epithelium). Gastritis variables (inflammation scores) were higher, and more frequent lymphocyte aggregates, in +ve cases, where a locally response was consistently elicited. Cag A status (6 Cag A +ve/14 Hp+ve studied cases) was not specifically associated with local humoral or cellular responses. Comments: These preliminary results confirm that a local specific humoral response (both IgG, IgA) is elicited in children with Hp infection, in parallel with a systemic response, and correlating with histology. Additionally, a mucosal response involving predominantly lamina propria T lymphocytes and plasmocytes, was a consistent finding in pediatric Hp associated gastritis. Their pathogenic significance and relevance to clinical outcome deserves elucidation from further studies at this age group, including characterization of antigenic specificity and cytokine profile. Supported by Comissão de Fomento de Investigação em Cuidados de Saúde.