CD40LG and infection: However, the following major limitations have been noted: MAT cannot be used for immediate case identification because it is insensitive in early infection [11]; it is not suitable for epidemiologic studies [18]; it is unable to distinguish between IgM and IgG [19]; it requires maintenance of large collections of different Leptospira serovars that can only be cultured in expensive specialized reference laboratories managed and operated by highly trained personnel.