Characterization of genetic humanized mice with transgenic HLA DP401 or DRA but deficient in endogenous murine MHC class II genes upon Staphylococcus aureus pneumonia

Staphylococcus aureus can cause serious infections by secreting many superantigen exotoxins in "carrier" or "pathogenic" states. HLA DQ and HLA DR humanized mice have been used as a small animal model to study the role of two molecules during S. aureus infection. However, the contribution of HLA DP to S. aureus infection is unknown yet.

These humanized mice will be an invaluable mouse model to resolve the pathological mechanism of S. aureus pneumonia and study what role DP molecule plays in S. aureus infection.

In this study, we have produced HLA DP401 and HLA DRA0101 humanized mice by microinjection of C57BL/6J zygotes. Neo-floxed IAβ+/- mice were crossbred with Ella-Cre and further crossbred with HLA DP401 or HLA-DRA0101 humanized mice. After several rounds of traditional crossbreeding, we finally obtained HLA DP401-IAβ-/- and HLA DRA-IAβ-/- humanized mice, in which human DP401 or DRA0101 molecule was introduced into IAβ-/- mice deficient in endogenous murine MHC class II molecules. A transnasal infection murine model of S. aureus pneumonia was induced in the humanized mice by administering 2 × 108 CFU of S. aureus Newman dropwise into the nasal cavity. The immune responses and histopathology changes were further assessed in lungs in these infected mice.

We evaluated the local and systemic effects of S. aureus delivered intranasally in HLA DP401-IAβ-/- and HLA DRA-IAβ-/- transgenic mice. S. aureus Newman infection significantly increased the mRNA level of IL 12p40 in lungs in humanized mice. An increase in IFN-γ and IL-6 protein was observed in HLA DRA-IAβ-/- mice. We observed a declining trend in the percentage of F4/80+ macrophages in lungs in HLA DP401-IAβ-/- mice and a decreasing ratio of CD4+ to CD8+ T cells in lungs in IAβ-/- mice and HLA DP401-IAβ-/- mice. A decreasing ratio of Vβ3+ to Vβ8+ T cells was also found in the lymph node of IAβ-/- mice and HLA DP401-IAβ-/- mice. S. aureus Newman infection resulted in a weaker pathological injury in lungs in IAβ-/- genetic background mice.