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1/4. Combined immunodeficiency associated with increased apoptosis of lymphocytes and radiosensitivity fibroblasts.

    Severe immunodeficiency characterized by lymphopenia was found in two siblings, one of whom was examined in detail. The calcium flux, pattern of tyrosine phosphorylation of proteins, and interleukin 2 (IL-2) production and proliferation in response to mitogens suggested that the peripheral blood T cells activated normally. The peripheral blood T cells were shown to have an activated phenotype with increased expression of CD45RO and CD95/Fas. Increased spontaneous apoptosis occurred in unstimulated lymphocyte cultures. The elevated apoptosis was not due to alterations in expression or to mutations in Bcl-2, Bcl-X(L), or Flip, nor could the spontaneous apoptosis be prevented by blocking Fas, suggesting that it was independent of Fas signaling. This is the first inherited combined immunodeficiency associated with impaired lymphocyte survival. fibroblasts derived from the patient showed appreciable radiosensitivity in clonal assays, but apoptosis was not elevated. Our results show that the fibroblasts represent a new radiosensitive phenotype not associated with cell cycle checkpoint defects, V(D)J recombination defects, or elevated chromosome breakage. We suggest that the affected gene plays a role in an undetermined damage response mechanism that results in elevated spontaneous apoptosis in lymphoid cells and radiosensitivity in fibroblasts.
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keywords = apoptosis
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2/4. autoimmune lymphoproliferative syndrome associated with severe humoral immunodeficiency and monoclonal gammopathy.

    A boy of Caucasian origin with a new subtype of autoimmune lymphoproliferative syndrome (ALPS) is described. The clinical picture was dominated by chronic noninfectious lymphadenopathy, splenomegaly, and recurrent bacterial infections. At the age of 6 the patient died of pneumococcal meningitis. Laboratory investigation disclosed impaired apoptosis in both B- and t-lymphocyte subsets and expanded populations of CD3 CD4-CD8- T lymphocytes. Furthermore, marked dysregulation of humoral immune responses with transient expansion of monoclonal B cells, corresponding monoclonal gammopathy, and the presence of autoantibodies was found. Functional and molecular analysis revealed that Fas protein expression was normal, a mutation in the Fas gene was not found. Moreover, transcription of the downstream effector caspase-10 was unremarkable. This patient is unique compared to previously described patients as severe humoral immunodeficiency and monoclonal gammopathy are usually not described in patients with ALPS. This case points out the important role of apoptosis in regulating the degree of humoral immune responses at a clonal level in humans and gives further evidence for the phenotypic diversity of ALPS.
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keywords = apoptosis
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3/4. Combined immunodeficiency phenotype associated with inappropriate spontaneous and activation-induced apoptosis.

    Programmed death of T cells has been proposed as one of the mechanisms by which hiv induces a decline in the number and functions of T cells in advanced AIDS. In this study we report on a patient affected by a congenital form of combined immunodeficiency presenting as a profound T cell activation deficiency. Subsequently, a gradual loss of T cells occurred, eventually resulting in a classical form of severe combined immunodeficiency (SCID). In this patient a sizeable fraction of apoptotic cells was documented in the first phase of the disease by either propidium iodide staining or dna fragmentation analysis. The presence of anergic T cells of maternal origin and engrafted in the child was excluded by analysis of DNA polymorphic regions. At 4 years of age the patient died of disseminated interstitial pneumopathy, while still awaiting an HLA-matched bone marrow transplantation. On the occasion of a new pregnancy in the mother, the prenatal immunological evaluation of the female fetus revealed a T B SCID phenotype. This is the first observation of a primary immunodeficiency associated with inappropriate apoptosis.
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keywords = apoptosis
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4/4. in vitro cell death of activated lymphocytes in Omenn's syndrome.

    Omenn's syndrome (OS) is characterized by erythrodermia, hepatosplenomegaly, lymphadenopathy, hypereosinophilia and elevated IgE levels associated with increased susceptibility to severe infections. Peripheral blood T cells, though usually present in normal number, show an activated phenotype (including an increased expression of CD95/Fas), a Th2 pattern of cytokine secretion and defective proliferative response to mitogens. In this report, we demonstrate that T cells from patients with OS undergo an excessive cell death in vitro resulting from two mechanisms. First, a substantial number of peripheral blood lymphocytes from OS patients die in unstimulated cultures (p = 0.009 vs. healthy controls). This spontaneous apoptosis is associated with reduced expression of bcl-2 gene product (p < 0.05) and can be prevented by addition of interleukin (IL)-2 (which also prevents down-modulation of bcl-2), while is independent from CD95 signaling. Second, lymphocytes from OS patients are highly susceptible to activation-induced cell death (AICD) induced with mitogens. This mechanism is largely independent from IL-2, while it can be significantly inhibited blocking CD95 with an IgG2b monoclonal antibody (mAb). The dependence of AICD from signals transduced via CD95 was confirmed showing that cross-linking CD95 with an IgM mAb induces a higher cell death in purified CD4 CD45R0 cells from OS patients than in controls (comparable for CD95 expression). Both mechanisms of cell death observed in this study result from lymphocyte hyperactivation occurring in vivo in these patients and may contribute to functional T cell defects of OS.
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keywords = apoptosis
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