G F Bottazzo

Role of aberrant HLA-DR expression and antigen presentation in induction of endocrine autoimmunity.

Immune responses are initiated by HLA-DR+ cells, which present antigen to T cells. Observations that HLA-DR may be experimentally induced on thyroid epithelium and that HLA-DR occurs on thyrocytes in autoimmune thyroid diseases suggest a mechanism of autoimmunity with special relevance to organ-specific diseases. This involves the local aberrant expression of HLA-DR antigens by epithelial cells and their subsequent capacity to present autoantigens occurring on their surfaces to T lymphocytes. For autoantigens which T cells recognise infrequently because of their restricted tissue location and low concentration in the circulation, T-cell tolerance is unlikely, and so induction of autoreactive T cells would occur. Because interferon is the best known inducer of DR antigen expression and viral infections may predate endocrine autoimmunity, the following sequence seems likely: local viral infection which causes interferon production, or other local environmental factors which would induce DR expression, presentation of autoantigens, and subsequent autoimmune T-cell induction. These T cells would activate effector B and T cells. Whether the initial induction of autoimmune T cells leads to autoimmune disease would depend on factors such as abnormalities of the suppressor T-cell pathway, reported to coexist with autoimmunity and necessary to induce autoimmune disease in mice. This mechanism of autoimmune disease induction explains vague associations with viral infections and long latency periods before disease becomes manifest and gives a simple explanation for the well-documented association between HLA-DR and autoimmune diseases in man.

AUTOANTIBODIES TO PROLACTIN-SECRETING CELLS OF HUMAN PITUITARY

A new autoantibody which reacted with anterior-pituitary tissue was deteected by immunofluorescent staining. Of 287 patients having one or more autoimmune endocrine diseases, sera from 19 reacted with pituitary glands obtained at hypophysectomy for breast cancer. Using specific rabbit antibodies to each of the six pituitary hormones and rhodamine-labelled goat-anti-rabbit-immunoglobulin (Ig) followed on the same unfixed cryostat section by a patientss serum counterstained with fluorescein-conjugated sheep-anti-human-Ig, it was posssible to show that the autoantibodies reacted specifically with the hypertrophied prolactin cells in these glands. The antibodies, belonging to the 3 main Ig classes, were complement fixing, with titres varying from 1 to 80. Double staining of prolactin cells and analogy with other autoimmune systems suggested that the antigen is in cytoplasmic organelles involved in the synthesis or delivery of the hormone. No pituitary antibodies were found in panhypopituitary cases, but there are indications that antibodies to other pituitary cells exist in some sera and that an autoimmune process may account for some cases of isolated pituitary hormone defects occurring in adult life.

Islet cell antibodies and diabetes mellitus in Pima Indians.

SummaryPancreatic islet cell antibodies and 12 other autoantibodies were measured at the time of diabetes diagnosis in 46 Pima Indians, aged 17–47 years, and in 46 age-sex matched non-diabetic controls. Islet cell antibodies were found in only two diabetics, aged 20 and 25, compared with none of 46 controls. Neither of the subjects with islet cell antibodies had other autoantibodies. At least one type of autoantibody was found in 14 (30%) of the diabetics and in 14 controls, but none was significantly associated] with diabetes. This study indicates that diabetes in the Pima Indians, even those with an onset below 25 years of age, is almost entirely of type II, in that the disease is not associated with islet cell antibodies, ketoacidosis, or insulin dependence.

DETECTION OF THYROID GROWTH IMMUNOGLOBULINS (TGI) BY [3H]‐THYMIDINE INCORPORATION IN CULTURED RAT THYROID FOLLICLES

A new bioassay is described for detecting the growth stimulating immunoglobulins (TGI)* that contribute to goitre formation in human thyroid autoimmune diseases. It measures the incorporation of tritiated thymidine into intact rat thyroid follicles grown in tissue culture. This radiometric assay demands much less technical skill than the cytochemical bioassays (CBA) previously employed. It has good reproducibility and the techniques and apparatus are available in many clinical laboratories.

THE INVOLVEMENT OF THE PENTOSE SHUNT IN THYROID METABOLISM AFTER STIMULATION WITH TSH OR WITH IMMUNOGLOBULINS FROM PATIENTS WITH THYROID DISEASE. 1. THE GENERATION OF NADPH IN RELATION TO STIMULATION OF THYROID GROWTH

It has been shown previously that both thyrotrophin (TSH), and also immunoglobulins (Ig) derived from patients with goitrous Graves’disease, stimulate DNA‐synthesis in guinea‐pig thyroid tissue maintained in vitro. Here we describe the use of the same in vitro system and methods of quantitative cytochemistry to test the effect of these substances on the generation of NADPH, which is another indicator of the potential for growth. As could be predicted by its trophic action, TSH stimulated the generation of NADPH by glucose 6‐phosphate dehydrogenase. The Ig‐fraction from normal subjects depressed this activity. The Ig‐fraction from Graves’disease patients with goitres stimulated the generation of NADPH, whereas the Ig from patients with Graves’disease but with minimal enlargement of the thyroid gland behaved like normal Ig. A similar lack of stimulation was found with Ig from patients with Pendreds syndrome, other dyshormonogenetic goitres, and autonomous single adenomas. In all specimens tested, there was good correlation between the amount of DNA‐synthesis, measured by Feulgen cytophotometry, and the activity of glucose 6‐phosphate dehydrogenase activity that generated NADPH. These results support the concept that there is a distinct type of autoantibody that influences thyroid growth.

Suppression of HLA class II expression on thyrocytes by interferon-alpha 1.

Inappropriate expression of HLA class II molecules by human thyroid epithelial cells (thyrocytes) is commonly associated with autoimmune thyroid disease. HLA class 11 expression can be modulated in thyrocytes in vitro by a variety of substances: in particular, it is readily induced by interferon‐gamma (IFN‐γ). Here we show that recombinant IFN‐α1 (rIFN‐α1) does not induce HLA class II expression by thyrocytes. but rather it suppresses the induction of such expression by rIFN‐γ. Similar effects were observed with IFN‐α derived from a lymphoblastoid cell line. The effect of rIFN‐α1 on thyrocytes differs from its effect on human monocytes, reported by others, in which it was found to enhance the expression of HLA class II. Thus, rIFN‐α1 appears to have a differential effect on HLA class II expression, depending on the cell type involved.

THE INVOLVEMENT OF THE PENTOSE SHUNT IN THYROID METABOLISM AFTER STIMULATION WITH TSH OR WITH IMMUNOGLOBULINS FROM PATIENTS WITH THYROID DISEASE. II. THE REOXIDATION OF NADPH AND STIMULATION OF HORMONE SYNTHESIS

Reducing equivalents derived from the tissue re‐oxidation of NADPH (NADPH‐diaphorase) have been implicated in the peroxidation that is involved in the organification of iodine in the production of thyroid hormones. Immunoglobulin (Ig) fractions from patients with thyroid diseases and from normal controls, in a standard dose of 125 μg/ml and 0±3 μ/ml thyrotrophin (TSH) were incubated with segments of guinea‐pig thyroid gland maintained in vitro. A quantitative cytochemical study was made on how these fractions influenced the enzyme activity. A good correlation was found between the ability of such Ig fractions to stimulate the NADPH‐diaphorase activity and (1) the degree of hyperthyroidism in the patients and (2) the amount of T3 secreted by the thyroid segments in vitro.