CARTOONS - The RIP-LCMV Model for Type 1 Diabetes

Attached is some really neat info on RIP-LCMV mice.  RIP-LCMV Mouse Model

 The RIP-LCMV mouse model was created to break tolerance to a defined target autoantigen expressed by b-cells through a viral infection. Such a target antigen represents a component of ‘self’ and therefore the host is ignorant or tolerant to that antigen.

Initiation of autoimmunity by virus-infection is twofold: First, the infection causes an activation of the innate immune system resulting in an inflammatory response involving the release of chemokines and cytokines. Those inflammatory factors in turn attract and activate leukocytes to the site of infection in a non-specific manner. Second, the presence of an identical antigen on both the b-cells and the infecting virus focuses this non-specific innate immune response specifically on the target antigen and thus breaks self-tolerance. Hence, after elimination of the intruding virus, the awakened immune response concentrates on the remaining transgenic target antigen expressed by the b-cells resulting in T1D. This scenario was experimentally reconstructed in the labs of Michael Oldstone (Scripps, La Jolla, CA) (Oldstone et al. (1991) Cell 65: 319-331) and Rolf Zinkernagel (Zurich, Switzerland) (Ohashi et al (1991) Cell 65: 305-317) in the early 1990’s.

By using the rat insulin promoter (RIP) they created transgenic mice whose pancreatic b-cells expressed either the nucleoprotein (NP) or the glycoprotein (GP) of LCMV as defined target antigens. Expression of either target antigen per se does not lead to b-cell dysfunction, islet cell infiltration, hyperglycemia, or spontaneous activation of autoreactive lymphocytes. However, infection with LCMV results in T1D in >95% of RIP-LCMV mice.  

Just as proposed for human T1D, the onset of diabetes in RIP-LCMV mice depends on the action of both, autoreactive CD4 and CD8 T-cells and correlates with the numbers of auto-aggressive lymphocytes generated. In accordance, the incidence of disease varied between the individual transgenic lines ranging from 2 weeks (RIP-GP lines) to 1-6 months (RIP-NP lines). Further studies revealed the mechanism involved in the rapid compared to the slow onset diabetes: Transgenic lines expressing the LCMV-GP transgene exclusively in the b-cells of the islets manifested rapid-onset T1D (10-14 days after viral challenge). In these lines the high systemic numbers of auto-aggressive CD8 T-cells were sufficient to induce diabetes and did not require help from CD4 cells. In contrast, in lines expressing the LCMV-NP transgene in both the b-cells and in the thymus, T1D took longer to occur after subsequent LCMV challenge. Several lines of evidence indicated that in RIP-NP mice the anti-self (viral) CTL were of lower affinity and that CD4 T-cells were essential to generate anti-self (viral) CD8 lymphocyte-mediated T1D. In addition, mouse models in which transgene-encoded ‘target-antigens’ are expressed in the pancreatic b-cells, such as the RIP-LCMV and the INS-HA mouse, have demonstrated that the presence of autoaggressive T-cells alone is not enough to cause disease. Unspecific ‘bystander factors’, such as cytokines and chemokines generated during the acute inflammation after LCMV infection, are important to drive the autoaggressive response (b-cell destruction) in ‘antigen-specific’ models for T1D.

Figure 2: Fast vs. slow onset model for type 1 diabetes

LCMV-GP is not expressed in the thymus of RIP-LCMV-GP mice and thus, LCMV-GP-specific CD8 T-cells of high affinity are released into the periphery resulting in fast destruction of LCMV-GP expressing beta-cells upon LCMV-infection and subsequently a fast-onset diabetes. In contrast, expression of LCMV-NP within the thymus of RIP-LCMV-NP mice induces the deletion of autoaggressive CD8 T-cells with high affinity. Only LCMV-NP-specific CD8 T-cells of low- or medium affinity are released into the periphery. Therefore the destrcution process of the insulin-producing beta-cell is delayed and depends on CD4 T-cell help resulting in a slow-onset type of diabetes.

COOL CARTOON

Figure 3: Immunopathogenic events following LCMV-infection in the RIP-LCMV model

LCMV-infection of the pancreas causes the release of ‘pro-inflammatory’ cytokines, such as TNFa, by resident macrophages. In turn, chemokines are released by activated endothelial cells as well as b-cells. Among them CXCL10 is the earliest chemokine to be expressed leading to high local concentrations at a very early time after LCMV-infection. CXCL10 predominantly attracts activated T-cells of the more aggressive Th-1 phenotype, which migrate into the inflamed tissue. Infiltrating LCMV-specific T-cells start destroying some b-cells in a perforin dependent manner. At a later stage further presentation of LCMV- and other islet antigens by professional antigen presenting cells, such as dendritic cells (DCs) leads to further proliferation and expansion of the autoaggressive T-cell repertoire. Islet antigen-specific, aggressive T-cells together with unspecific bystander factors destroy most of the remaining b-cells resulting in overt diabetes.