Isogenic serotypes of Borrelia turnicatae show different localization in the brain and skin of mice

Mice with severe combined immunodeficiency (scid mice) and infected with th e relapsing fever agent Borrelia turicatae develop manifestations that rese mble those of disseminated Lyme disease. We have characterized two isogenic serotypes, A and B, which differ in their variable small proteins (Vsps) a nd disease manifestations. Serotype A but not serotype B was cultured from the brain during early infection, and serotype B caused more severe arthrit is, myocarditis, and vestibular dysfunction than serotype A, Here we compar ed the localization and number of spirochetes and the severity of inflammat ion in scid mice, using immunostained and hematoxylin-and-eosin-stained cor onal sections of decalcified heads, Spirochetes in the brain localized pred ominantly to the leptomeninges, and those in peripheral tissues localized m ainly to the extracellular matrix, There were significantly more serotype A than B spirochetes in the leptomeninges and more serotype B than A spiroch etes in the skin, The first tissue where spirochetes were observed outside the vasculature was the dura mater, Inflammation was more severe in the ski n than in the brain, VspA, VspB, and the periplasmic flagellin protein mere expressed in all tissues examined, These findings indicate that isogenic b ut antigenically distinct Borrelia serotypes can have marked differences in their localization in tissues.