Immune alterations associated with T lymphocyte activation and regulation in retinitis pigmentosa patients

A novel homozygous splice site variant in ARL2BP causes a syndromic autosomal recessive rod-cone dystrophy with situs inversus, asthenozoospermia, unilateral renal agenesis and microcysts

BACKGROUND

This report presents a clinical case of syndromic rod-cone dystrophy due to a splice site variant in the ARL2BP gene causing situs inversus, asthenozoospermia, unilateral renal agenesis and microcysts. The presence of renal agenesis and cryptorchidism expands the clinical manifestations due to ARL2BP variants. The detailed, long-term follow-up contributes valuable insights into disease progression, aiding clinical diagnosis and patient management.

CASE PRESENTATION

The male patient complained of photophobia as the first symptom when he was 20 years old followed by nyctalopia, loss of central visual acuity and peripheral visual field ten years later. Genetic analysis identified a likely pathogenic homozygous variant (c.294-1G > C) involving the splicing acceptor site of intron 4. Reported symptoms together with full-field stimulus threshold testing, electroretinogram and advanced multimodal imaging allowed us to recognize the typical characteristics of a mixed retinal dystrophy. Despite the end-stage retinal disease, this patient still retained a useful residual vision at 63 years and had a slow disease progression during the last 5 years of evaluation.

DISCUSSION AND CONCLUSIONS

Our findings underscore the variable clinical presentation of ARL2BP variants, emphasizing the importance of a nuanced approach in diagnosing and managing patients. The presence of renal cysts warrants consideration of a differential diagnosis, particularly with Senior-Loken (SLS), Bardet-Biedl (BBS) and Joubert syndromes (JS) but also with Short Rib Thoracic Dysplasia 9, highlighting the need for careful phenotypic evaluation in these cases.

A review of the immunologic findings observed in retinitis pigmentosa

Most patients suffering from retinitis pigmentosa (RP) inherit the disorder; however, the immune-pathologic features associated with this disease have yet to be extensively studied. Six reports correlate antiretinal immune activity with vision deterioration in RP patients. Some of these patients have sporadic RP that occurs in excess of expected gene segregation during inheritance. The hypothesis that a primary immune-mediated disease process occurs in this sporadic group is supported by significant associations of RP with autoimmune endocrinopathies and other immune-related conditions or factors; however, no immunologic difference regarding RP family history is reported in the peripheral blood studies of RP patients. Twenty-one percent to 51% of RP patients display antiretinal antibodies, whereas 19-58% have antiretinal lymphocyte reactivity to retinal extract, and 60-85% have activated T cells. Mutations in animal models of RP have been shown to cause endoplasmic reticulum stress that may initiate immunopathology for genetic RP, but oxidative stress also encourages immune cytotoxicity. In addition, necrotic cell death is evident, which promotes inflammatory conditions. We review mechanisms and evidence for an occult inflammation in genetic RP and examine reports of efficacy in retarding RP progression with anti-inflammatory agents in clinical trials.

Systemic immunostimulation after retinal laser treatment in retinitis pigmentosa

Systemic immunostimulation followed an experimental treatment trial of scatter argon laser photocoagulation directed to the retina of one eye of 10 patients with heredo-degenerative retinitis pigmentosa (RP). Significantly increased RP lymphocyte CD25, CD26, and CD4/CD26 activation epitope expressions over prelaser values and controls were found with a normalization of soluble interleukin-2 receptor secretion after laser treatment. Serum interferon-gamma was low both pre- and postlaser. Interestingly, when a panel of viral antibodies was tested, only those to rubella virus were elevated in the early postlaser period. The character of RP immunostimulation after laser-induced inflammation could be consistent with an antigenic stimulus from laser-released retinal proteins which might be of autoimmune or latent infectious origin. Enhanced immune responses may be a common but unrecognized sequellae of retinal laser.

Expression of Schwann cell and peripheral T-cell activation epitopes in hereditary motor and sensory neuropathy

To evaluate possible immune-mediated mechanisms in hereditary motor and sensory neuropathy (HMSN-I, Charcot-Marie-Tooth syndrome), we examined class II major histocompatibility complex antigen expression (MHC-II, HLA-DR) in Schwann cells and peripheral lymphocyte T-cell (Ta1, CD26) activation in five unrelated adults with HMSN-I. Evidence of increased activation expression was found in both compartments but the pattern did not suggest a general state of hyperimmunity or appear related to clinical characteristics of HMSN. Significantly increased CD26+ T-cell activation and greater than normal fluctuation of values occurred intermittently in sequential tests of eight HMSN patients and at single time points in 24 others. The combined data, consistent with repeated stimulations of an immune reaction under normal feedback control, suggest that HMSN-I expresses some characteristics also found in autoimmune polyneuropathies.

Triggering of the proteinase dipeptidyl peptidase IV (CD26) amplifies human T lymphocyte proliferation

CD26 (Ta1, dipeptidyl peptidase IV) is a Mr 105,000 protein expressed at high levels on activated T lymphocytes and is a potential marker of memory T cells. Reciprocal immunodepletion and solid phase double determinant binding studies showed that mAb AC7 and the CD26-specific mAb anti-Ta1 reacted with spatially distinct sites on the same molecule. The proteinase dipeptidyl peptidase IV (DPP IV) was immunoprecipitated with mAb AC7 and its enzymatic activity directly assayed using an enzyme overlay membrane system. High levels of DPP IV activity were detected on the T cell tumor line CCRF-HSB-2 and on PBMC stimulated by a variety of methods. By itself, soluble mAb AC7 was not mitogenic for T cells but enhanced T cell proliferation that resulted from treatment with phorbol myristic acetate (PMA) in the presence of accessory cells. T cell proliferation was also induced by co-immobilized mAb AC7 and mAb OKT3 (anti-CD3). Cultures of T cells growing in the presence of IL-2 responded with accelerated growth when exposed to a combination of immobilized mAb AC7 and soluble mAb OKT3, a result not seen with freshly isolated T cells.