Insulin selectively primes Th2 responses and induces regulatory tolerance to insulin in pre-diabetic mice

Abstract

There is conflicting information as to the existence, prevalence and phenotype of cellular immune responses to insulin in pre-diabetic rodents and humans [1±6]. Furthermore, little is known about the immunological impact of insulin administration, other than it can boost insulin autoantibody levels ([7] and references therein). The subcutaneous administration of soluble antigen has been traditionally thought to be only weakly immunogenic in naive animals, necessitating the use of adjuvants to prime significant immune responses. However, it has recently been shown that the subcutaneous administration of prototypic soluble foreign antigens can prime naive T cells toward a Th2 phenotype [8]. This finding raises the question whether the subcutaneous administration of self-antigens, such as insulin to pre-diabetic and diabetic individuals, also induces Th2 responses. If insulin administration does have an immunological impact, the nature of this response (Th1/ Th2) may depend on whether an autoimmune response to insulin is already established and the phenotype of this response. If a memory Th1 response to insulin is present in pre-diabetic and diabetic animals, insulin injection may boost this pro-inflammatory response. On the other hand, if insulin adminis- Diabetologia (1998) Summary Little is known about the immunological impact of insulin administration other than it can boost insulin autoantibody levels. In particular, while the subcutaneous administration of a soluble foreign antigen (without adjuvant) is generally only weakly immunogenic in a naive animal, it is unknown what effect the subcutaneous administration of a soluble self-antigen has in animals with established autoimmune responses to the antigen. Addressing these questions in pre-diabetic nonobese diabetic (NOD) mice, we examined the effects of administering insulin, as well as the metabolically inactive B-chain of insulin, on insulin-specific cellular and humoral immune responses. We show that pre-diabetic NOD mice have a spontaneous Th1-biased response against insulin. Administering insulin, or the insulin B-chain, rather than boosting the established Th1 response, primed Th2 cellular and humoral immunity to insulin, shifting the predominant insulin response toward a Th2 phenotype. Despite the presence of a Th1 response against insulin, insulin treated mice failed to mount proliferative T-cell responses following immunization and challenge with insulin, demonstrating that the treatment induced an active form of tolerance to this autoantigen. Thus, the subcutaneous administration of a soluble antigen can engage Th2 responses and induce self-tolerance, even after the establishment of autoreactive Th-1 responses. Such immune deviation and induced regulatory tolerance may contribute to the protective effects of prophylactic insulin therapy, as well as the establishment of a ªhoneymoonº phase in new-onset insulin-dependent diabetic patients. [Diabetologia (1998) 41: 237±240]

Peptide and Major Histocompatibility Complex–Specific Breaking of Humoral Tolerance to Native Insulin With the B9-23 Peptide in Diabetes-Prone and Normal Mice

“…This may correlate with the observation that a single injection of the peptide in IFA at 4 weeks of age can inhibit the development of diabetes for months. As described in previous reports (26), IAAs in both unmanipulated NOD mice and NOD mice treated with B9-23 peptides in IFA were of the IgG1 subclass (data not shown), whereas for BALB/c mice after immunization with B9-23 peptide, antibodies were predominantly IgG1, but a lower level of IgG2a was also induced.…”

“…Insulin, given subcutaneously, intranasally, or orally, can prevent diabetes in NOD mice (23,24). Administration of insulin B-chain or B-chain peptide B9-23 as well as insulin can prevent diabetes in NOD mice (14,25), and soluble insulin B-chain administration boosts the anti-insulin autoantibody response in the NOD mouse (26). IAAs in humans with type 1 diabetes fail to bind isolated insulin B-chain (18).…”

Exposure to exogenous insulin promotes IgG1 and the T-helper 2-associated IgG4 responses to insulin but not to other islet autoantigens.

“…Immunization with insulin, GAD, or specific autoantigen peptides at an early age can delay and even prevent the onset of diabetes in NOD mice (2)(3)(4)(5). Immunization appears to alter the phenotype of T-cells found in islet infiltrates to one that is Th2-dominated and induces an antibody response typical of Th2 immunity (6). Therefore, the protection offered by immunization with antigens has been suggested to be due to a spreading immune deviation away from Th1 toward Th2, as a result of selective Th2 priming by antigen (6,7).…”

“…The issue of whether protection in humans is also through induction of protective Th2 immunity has not been examined. In mice, Th2 immune responses are characterized by antibodies of the IgG1 subclass (12,13); accordingly, IgG1 antibodies are found after administration of insulin (6). Although distinct antibody subclass associations with Th1 or Th2 immunity are not as clear in humans as they are in mice, the Th2 cytokine interleukin (IL)-4 can induce both IgE and IgG4 antibody production, and these antibodies are characteristic of the Th2-dominated response of atopy (14).…”

“…The diabetes protection after insulin treatment in mice can be transferred by CD4 spleen cells, and it is thought that the major protective effect by insulin therapy is through the induction of regulatory Th2 CD4 cells (22)(23)(24)(25). Supporting this view is the observation that the antibody response to insulin in these models is predominantly of the Th2-associated mouse IgG1 and IgG2b subclasses (6). Therefore, we studied the IgG subclass of insulin antibodies in humans to see whether there is evidence of a Th2-biased response to exogenous insulin therapy, which would further support its prophylactic use for disease suppression.…”