Antigen binding proteins and assays

An antigen binding protein which binds to Protein E at one or more of amino acid residues within I41 to Y49 (e.g. SEQ ID NO:

• 133) and Y141 to A154 (e.g. SEQ ID NO:
• 134) of Protein E, said antigen binding protein comprising a VH region comprising a sequence at least 80% identical to the sequence of SEQ ID NO:
• 124;
• and/or a VL region comprising a sequence at least 80% identical to the sequence of SEQ ID NO:
• 129.

An antigen binding protein comprising:

• (i) any one or a combination of CDRs selected from CDR-H1 (SEQ ID NO:
• 125), CDR-H2 (SEQ ID NO:
• 126) or CDR-H3 (SEQ ID NO:
• 127), and/or CDR-L1 (SEQ ID NO:
• 130), CDR-L2 (SEQ ID NO:
• 131) or CDR-L3 (SEQ ID NO:
• 132) or
• (ii) a CDR variant of (i), wherein the variant has 1, 2, or 3 amino acid modifications in each CDR, which is able to bind to Protein E at one or more of amino acid residues within I41 to Y49 and Y141 to A154 of Protein E (e.g. SEQ ID NO:
• 133 and SEQ ID NO:
• 134).