Prior Cryptosporidium Infection Leads to Protective Th-1 Type Mucosal Immunity Despite Protein Malnutrition

Cryptosporidium is a major cause of childhood diarrhea and stunting in resource-limited countries.  Malnutrition increases risk of cryptosporidiosis and could impair mucosal vaccine uptake.  The immunologic consequences of malnutrition on mucosal immune responses, and specifically related to Cryptosporidium infection, are poorly understood. Malnourished children with cryptosporidiosis have increased fecal IL-13, which has been interpreted to indicate a Th-2-biased response.  Using a murine model of protein malnutrition (PM), we show that despite decreased baseline IFN-𝛾, and severe enteropathy, Th-1 type immune responses in cryptosporidiosis are enhanced.  Primary infection with 10⁶ C. parvum challenge conferred resistance to parasitism and weight loss after secondary challenge with 10⁷ C. parvum 21 days later.  C. parvum 10⁶ challenge resulted in minimal inflammation at three days post-infection, but through 23 days post-infection, CCL5 progressively increased (68.83 vs 38.43 pg/ml, P<0.05) and CD4⁺ and CD8⁺ cells, including those with a CD8⁺CD103⁺ phenotype, expanded within the lamina propria.  At re-challenge, previously exposed mice had further increases in CCL5 (122.38 vs 34.61, P<0.001), as well as greater IFN-𝛾 (21.38 vs 11.47 pg/ml, P=0.056) and IL12p40 (26.17 vs 1.90 pg/ml, P<0.05) compared with primary infection. Re-challenge associated with significantly lower IL-13 (113.30 vs 0 pg/ml; P<0.05) than primary infection.  IL-4 and IL-5 were not elevated, suggesting a non-Th2 source of IL-13.  This is the first model to demonstrate protective mucosal immunity in cryptosporidiosis despite PM. Future investigations will confirm whether the CD8⁺CD103⁺ cells have a tissue-resident memory phenotype and are protective, and whether IL-13 promotes barrier dysfunction in cryptosporidiosis.