LAG3 Gene and Early Onset of Type 1 Diabetes

The lymphocyte activation gene-3, LAG3, is a significant regulator of the immune system and recently has been concretely attributed to development in Type 1 Diabetes in diabetes prone mice. Type 1 Diabetes is an autoimmune disease in which cells of the body are mistaken as pathogens and destroyed by the immune system. In Type 1 Diabetes, the cells that are destroyed are the insulin-producing beta cells. This disease is generally characterized by insulitis and beta-cell autoantibodies (Van den Driessche et. al, 2009).

LAG3 may be responsible for the malfunctioning of the immune system and the onset of Type 1 Diabetes. LAG3 plays a large part in regulating T cells, which are critical to fighting infections and diseases. LAG3 both regulates the numbers of T cells in the body and is required for the proper functioning of T cells and Natural Killer cells (Workman et. al, 2009). Moreover, many critical cell types in the immune system express LAG3, including CD4⁺ and CD8⁺ T cells, natural killer cells, and plasmacytoid dendritic cells (Workman et. al, 2009). These cells each play important functions in detecting pathogens throughout the body and carrying out the removal of harmful entities.

Lag3 deletion in normal mice has been documented to have minor noticeable changes, with little to no effect on the prevalence of diabetes development (Miyazaki et. al, 1996). However, it has been recently demonstrated that in autoimmune-prone conditions, LAG3 plays a critical role in an early onset of Type 1 Diabetes (Bettini et. al, 2011).

Bettini et. al used non-obese diabetic mice, or NOD mice, to test the control of LAG3 on three important types of cells in the immune system: T cells, natural killer cells and plasmacytoid dendritic cells (2011). NOD mice were the subjects of choice, for they are often used as a mouse model of Type 1 Diabetes (Crawford et al., 2011). Bettini et. al bred NOD mice with a Lag3 mutation, rendering the gene non-functional. The mice were then tested for diabetes onset at various points of development by analysis of urine samples and blood glucose levels.

The results were overwhelmingly significant. 100% of mice with mutated Lag3, compared to 15% of mice with properly functioning Lag3, rapidly developed diabetes. Furthermore, female mice with mutated Lag3 developed diabetes on average 10 weeks earlier than female mice with normal functioning Lag3. Males had even more drastic results, for mutated Lag3 males developed diabetes 14 weeks earlier. Therefore, the mutation of Lag3 resulted in an earlier onset of diabetes in both female and male mice (Bettini et. al, 2011).

This experiment also examined the results of blocking LAG3 in seven-week-old NOD mice. In a blocking experiment, LAG3 is still encoded properly by the genetic sequence, but it is prevented from being transcribed to produce a product, negating its function. Blocking the LAG3 gene lead to accelerated diabetes development by 8 weeks (Bettini et. al, 2011). From these results, it was further confirmed that the Lag3 plays a major role in the onset of Type 1 Diabetes.

LAG3 may function on the molecular level, changing the quantities of T cells as well as other immune cells in the body. T cells play a large role in the ability of the body to recognize foreign invaders and carry out measures to either kill or sequester harmful entities and mark them for clearance. There are two main subsets of T cells: helper T cells and cytotoxic T cells, also referred to as CD4⁺ T cells and CD8⁺ T cells respectively. Lag3 was determined to play a major molecular role in regulating T cells, perhaps affecting the development of diabetes (Bettini et. al, 2011). In Lag3 mutated mice, the total observed quantities of T cells were increased. Moreover, the mutation of Lag3 resulted in increased T cell infiltration, retention, and proliferation of CD4⁺ and CD8⁺ T cells in the pancreas (Bettini et. al, 2011). From these results, it is evident that Lag3 functions to control and maintain the amount of T cells present in the pancreas. Therefore, a mutation in Lag3 will result in T cell proliferation and an excess of T cells.

The individual function of Lag3 on CD4⁺ and CD8⁺ T cells was then analyzed. From adoptive transfer of mutated Lag3 CD4⁺ T cells into normal mice, there was noted to be an acceleration of disease. In fact, CD4⁺ T cells were found to be sufficient to drive the accelerated diabetes onset and incidence observed (Bettini et. al, 2011). CD8⁺ T cells were also found to accelerate the onset of diabetes, but to a lesser extent (Bettini et. al, 2011). Therefore, a mutation of LAG3 may impact disease development by altering the numbers of CD4⁺ T cells, although CD8⁺ T cells still have a minimal influence on the onset of disease.

This experiment continued to further test the conditions that may affect the onset of Type 1 Diabetes by measuring the presence of Ag-reactive T cells. Ag-reactive T cells are potentially pathogenic clones that have been associated with the progression of diabetes (Lieberman et. al, 2004). In this study, it was found that Ag reactive T cells were increased by 2 to 4-fold in mutated Lag3 mice (Bettini et. al, 2011). This demonstrates that LAG3 may have selective effect on more diabetogenic clones, providing a potential reason for the early onset of disease.

Other LAG3 expressing cells were analyzed, including natural killer cells and plasmacytoid dendritic cells. However, there was no significant increase in frequency of these cells and no other inconsistency with normal functioning LAG3 (Bettini et. al, 2011). More experiments on the influence of these cell types on the immune system should be performed, for even though the quantities of cell may not have differed, their effects within the immune system may be altered by the deletion of LAG3, resulting in further contribution to the early onset of diabetes observed in this study.

This study clearly identifies LAG3 is an important gene in the development of Type 1 Diabetes. A mutated LAG3 or the blocking of LAG3 increases an early onset of diabetes in mice that are prone to Type 1 Diabetes. The cause for the acceleration may be attributable to LAG3 altering the amounts of CD4⁺ and CD8⁺ T cells in the immune system, or Ag-reactive T cells.

This study notes the quantities of cell types affected by LAG3, but it does not examine the functionality of the cells. LAG3 has an effect on T cell quantities, but not natural killer cells and plasmacytoid dendritic cells. I believe it would be interesting and worthwhile to asses the effective functions of the produced natural killer cells and plasmacytoid dendritic cells, for I would not be surprised if they had an increased effect.

Identification of LAG3 as an important component for the development of Type 1 Diabetes may enhance the diagnosis and treatment of Type 1 Diabetes. The functioning of LAG3 in individuals can be assessed and allow for either early diagnosis of disease, or for preventative steps to be taken in order to prolong disease onset.

Works Cited:

Bettini M, Szymczak-Workman AL, Forbes K, Castellaw AH, Selby M, Pan X, Drake CG, Korman AJ, Vignali DA. Cutting edge: accelerated autoimmune diabetes in the absence of LAG-3. J Immunol. 2011 Oct 1;187(7):3493-8. Epub 2011 Aug 26. PubMed PMID: 21873518; PubMed Central PMCID: PMC3178660.

Crawford F, Stadinski B, Jin N, Michels A, Nakayama M, Pratt P, Marrack P, Eisenbarth G, Kappler JW. Specificity and detection of insulin-reactive CD4+ T cells in type 1 diabetes in the nonobese diabetic (NOD) mouse. Proc Natl Acad Sci U S A. 2011 Oct 4;108(40):16729-34. Epub 2011 Sep 26. PubMed PMID: 21949373.

Lieberman, S. M., T. Takaki, B. Han, P. Santamaria, D. V. Serreze, and T. P. DiLorenzo. 2004. Individual nonobese diabetic mice exhibit unique patterns of CD8+ T cell reactivity to three islet antigens, including the newly identified widely expressed dystrophia myotonica kinase. J. Immunol. 173:3347-3356.

Miyazaki, T., A. Dierich, C. Benoist, and D. Mathis. 1996. Independent modes of natural killing distinguished in mice lacking Lag3. Science 272:405-408.

Van den Driessche A, Eenkhoorn V, Van Gaal L, De Block C. Type 1 diabetes and autoimmune polyglandular syndrome: a clinical review. Neth J Med. 2009 Dec;67(11):376-87. Review. PubMed PMID: 20009114.

Workman, C. J., Y. Wang, K. C. El Kasmi, D. M. Pardoll, P. J. Murray, C. G. Drake, and D. A. Vignali. 2009. LAG-3 regulates plasmacytoid dendritic cell homeostatis. J. Immunol. 182:1885-1891.