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Editors Selection IGR 7-1

Basic research: Thymulin

Comment by Martin Wax on:

14030 Plasma thymulin and nerve growth factor levels in patients with primary open angle glaucoma and elevated intraocular pressure, Noureddin BN; Al-Haddad CE; Bashshur Z et al., Graefe's Archive for Clinical and Experimental Ophthalmology, 2006; 244: 750-752

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Thymulin, which is produced by specific epithelial cells of the thymus, is a zinc-activated metallopeptide that is involved in several aspects of intra- and extrathymic T-cell differentiation. Growing evidence suggests that thymulin is a key regulator of the body's neuroendocrine system and has regulatory interactions with many pituitary hormones. While many hypophyseal hormones such as growth hormone, prolactin and thyroxine regulate thymulin secretion, the hormone itself exerts a controlling feedback effect on its own secretion both in vivo and in vitro.

In the article by Noureddin et al. (802),concentrations of thymulin as well as nerve growth factor levels were assessed in the serum in 28 patients with newly diagnosed POAG and compared to values obtained in age and sex matched controls without ocular or systemic disease. For thymulin, a statistically significant elevation was observed in the POAG group (p < 0.001) with a mean level of 0.83 &plm; 0.40 pg/ml versus 0.23 &plm; 0.23 pg/ml in the controls. No significant results were noted when comparing mean NGF concentrations in the POAG and control patients.

An elevation of thymulin in theserum of POAG patients was found

While these observations are interesting, the role that thymulin might have in glaucoma remains unknown. In the past decade, there has been increasing evidence that abnormalities of the humoral and cellular immune system occur in selected patients with glaucoma. In fact, the suggestion has also been made that one day, it may be possible to exploit the body's innate defense immune mechanisms for therapeutic gain such as with immunization. The key issue for many of the observations in which immunodeficiencies in glaucoma patients have been reported, is whether these are primary insults, or part of the body's compensatory mechanisms in response to the insult. That is, are they cause or effect? Clarification of this issue would thus also be pertinent to the observation that serum thymulin levels appear to be 3 to 4 times higher in patients with glaucoma.

It would be fascinating to study thymulin serum levels more widely and correlate them to the changes in the T cell repertoire that have been demonstrated or remain to be studied in patients with glaucoma. One can also envision that it might be useful to look at thymulin levels as a function of intraocular pressure in patients with glaucoma, since this stress condition plays a key role in determining the cell fate of RGCs in which the apoptotic cascade is widely known to be highly immunoregulated. Although it was a brief report, the authors may have opened yet another pandora's box in glaucoma that will surely benefit from more articulating studies.

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