Wild-Type Mice Infected with One Strain of Influenza a Virus $\gamma$

Wild-type mice infected with one strain of Influenza A virus (PR8) by intranasal inoculation are protected from intranasal infection by a related Influenza A virus (Beijing) , a phenomenon known as cross-protection. These infections are generally localized to the upper respiratory tract. Mice with a homozygous single gene defect in 'gene X' have greatly impaired cross-protection to Influenza A-Beijing following immunization with Influenza A-PR8 by the intranasal route. Gene X likely encodes:

A) Fc receptor, Fc $\gamma$ RIIa
B) Complement receptor, CR1
C) TLR adapter protein, MyD88
D) Poly Ig receptor
E) AID