Autoimmune Lymphoproliferative Syndrome
University Medical Center Groningen
In the immune system, apoptosis counters the proliferation of lymphocytes to achieve
a homeostatic balance and also plays a central role in the selection of antigen specific T and B cells.
Apoptosis is a form of programmed cell death that is controlled by aspartate-specific cysteine proteases
called caspases. Mutations in genes involved in apoptosis have been identified as a cause or a
contributing factor in the development of hematopoietic diseases. Well-known examples are the bcl-2 and p53 genes, which are frequently involved in
the development and/or progression of lymphomas. Activated T cells express an apoptosis receptor
molecule termed Fas (CD95, Apo-1), which is a member of the tumor necrosis factor receptor family
(TNFRSF6). Cross-linking of Fas to the Fas ligand (CD95L) results in a functional trimeric structure of
the Fas protein. The intra-cellular domain of Fas, also known as the death domain, transduces a death
signal by recruiting Fas-associated death domain (FADD), caspase-8 and caspase-10 proteins into a
death-inducing signalling complex. Fas is normally expressed on activated T and B cells and plays an
important role in eliminating auto-reactive T cells and in the maintenance of the peripheral lymphocyte
Germ line mutations in the Fas gene have been observed in
autoimmune lymphoproliferative syndrome type I (ALPS Ia) . The mutations are generally small
deletions and point mutations that result in splicing errors or missense changes. Somatic Fas gene mutations have been identified in some malignant lymphomas and solid
tumors . Germ line mutation in the Fas-ligand gene, that induces
apoptosis upon binding to Fas, has been described in patients with systemic lupus erythematodes symptoms
and lymphadenopathy (ALPSIb) . Caspase 10 (Mch4/FLICE2) is a representative of the caspase family of
cysteine proteases, which plays a central role in the execution of apoptosis. At least two kindreds have
been reported, characterised by abnormal lymphocyte and dendritic cell homeostasis and immune regulatory
defects, which harboured independent missense mutations in the Caspase 10
gene . These mutations encoded amino acid substitutions that decrease Caspase activity and interfere
with death receptor-induced apoptosis, particularly that stimulated by Fas-ligand and TRAIL. Inherited
non-lethal caspase abnormalities can therefore cause pleiotropic apoptosis defects underlying
autoimmunity in ALPS type 2. Recently, also a kindred with mutations in the caspase
8 gene was described resulting in defective lymphocyte apoptosis and homeostasis but, unlike other
patients with ALPS, also defects in the activation of T and B cells and natural killer cells, resulting
in immunodeficiency . Cases with the symptoms of ALPS and deficiency of the Fas apoptosis pathway but
without Fas mutation were described by Dianzani and grouped as ALPS type 3.
Table 1: Classification of Autoimmune Lymphoproliferative Syndrome
|ALPS type 1a ||Fas gene mutation|
|ALPS type 1b || Fas ligand gene mutation|
|ALPS type 2 || Casp 8 or Casp 10 gene mutation|
|ALPS type 3 || No known gene mutations|
Recently a new symptom-complex was described, characterised by manifestations of autoimmune disease,
infectious lymphadenopathy, double negative T cells, and impaired activation-induced cell death that
developed in late adolescence . The main clinical features were recurrent bacterial infections with
subsequent lymphadenopathy due to autoimmune neutropenia. Laboratory tests revealed a large proportion
of TCRab positive, CD4 and CD8 negative T cells, and decreased apoptosis upon activation with
phytohemagglutinin and interleukin 2, but normal Fas-mediated apoptosis. Genetic investigations excluded
mutations in the Fas gene death domain and in the 4 exons of the Fas ligand gene. Despite unknown pathogenesis, this new syndrome may belong to
the growing group of diseases with defects in apoptosis.
Germline Fas Mutations and ALPS
Germline mutations of the Fas gene are associated with the development of
autoimmune lymphoproliferative syndrome (ALPS; Canale-Smith syndrome). The symptoms of the disease are
similar to those in lpr mice . Patients with ALPS usually have enlargement of the spleen and lymph
nodes, various manifestations of autoimmunity, and elevation of double negative T cells. The autoimmune
phenomena include thrombocytopenia and anemia. The anti-platelet antibodies associated with ALPS bind to
the same platelet glycoprotein complexes as those of idiopathic thrombocytopenic purpura patients. Most
ALPS patients have mutations in the death domain of the Fas gene. These
mutations are dominant negative, which can be explained by the for a functional Fas receptor essential
trimeric structure. The accumulation of double negative T cells is caused by loss of function of wild
type Fas. This loss prevents the elimination of auto reactive T cells and the maintenance of normal
lymphocyte homeostasis. The relationship between genotype, phenotype and disease penetrance is complex.
Within a family, individuals with the mutation may have severe symptoms, moderate symptoms or even no
symptoms at all. This suggests the contribution of one or more additional factors to the pathogenesis of
ALPS. Treatment strategies remain mostly targeted at the disease manifestations. The diagnostic
criteria for ALPS are summarised in table 2.
Table 2: Symptoms of Autoimmune Lymphoproliferative Syndrome
Hepatosplenomegaly & Lymphadenopathy
Proliferation of double negative (DN) T cells
Defective in vitro apoptosis (<50% of normal)
Autoimmune phenomena (anemia, thrombocytopenia)
The Double Negative Lymphocytes
Elevation of CD4 and CD8 negative (double negative, DN) T cells is one of the most characteristic
findings in patients suffering from autoimmune lymphoproliferative syndrome (ALPS). These DN T cells
usually bear a b T cell receptors (TCR), are negative for CD45R0, but positive for CD45RA. Initially
this phenotype was thought to be consistent with recent thymus emigrants. The expanded population of a b
DN T cells from ALPS patients has a remarkable uniform phenotype. This is in contrast to the small a b
DN T cell compartment in healthy individuals, that contains multiple immunophenotypically distinct
subpopulations. Current data indicate that a b DN T cells from ALPS patients are derived from cytotoxic
CD8 T cells, chronically activated in vivo, but anergic in vitro. Their anergic state may be related to persistent modifications of
O-linked carbohydrates on cell surface molecules, such as CD43 and CD45, as well as to the increased
levels of interleukin-10. The a b DN T cells are immunophenotypically and functionally similar to a b DN
T cells that accumulate in lpr and gld mice, which bear genetic mutations in Fas
(lpr) and FasL (gld). In these mice, TCRa b DN T cells express the
B-cell-specific CD45R isoform B220. TCRa b DN T cells of ALPS patients, with either Fas or FasL mutations, also express B220. In
addition, also similar to lpr/gld mice, they have an unusual population of B220-positive CD4(+) T cells
In a study on the immunophenotypic findings in 166 members of 31 families with ALPS type Ia, the ALPS
type Ia probands and relatives having both a Fas mutation and clinically
proven ALPS showed significant expansion of CD8 T cells, TCR a b DN T cells, TCRgd DN T cells, HLA-DR
positive CD3 T cells, CD8/CD57 T cells, and CD5 B cells. Relatives with Fas
mutations, but without all the required criteria for ALPS, also had expansions of CD8 T cells, TCRab DN T
cells, and TCRgd DN T cells. Interestingly, relatives without a Fas mutation and with no features of
ALPS (n = 65) demonstrated a small but significant expansion of CD8(+) T cells, both DN T cell subsets,
and CD5(+) B cells. As compared to unrelated healthy controls, lymphocyte subset alterations were
greatest in the probands, followed by the relatives with mutations and ALPS. Probands and relatives with
mutations and ALPS also showed a lower number of CD4/CD25 T cells that, in combination with an
independent increase in HLA-DR positive T cells, provided a profile predictive of the presence of
clinical ALPS. Because quantitative defects in apoptosis were similar in Fas mutation-positive relatives and in ALPS patients, factors other than modifiers
of the Fas apoptosis pathway must contribute to disease penetrance in ALPS.
In a recent case report a 6-month-old girl was described with an enlarged liver and spleen, cervical
lymphadenopathy, anemia, and thrombocytopenia since the age of 1 month . Immunohistochemical
analysis of an affected lymph node revealed a phenotype, i.e. presence CD3/CD57 DN T cell blasts,
consistent with the usual ALPS phenotype. Remarkably, the DN T cells in the lymph node stained positive
for TCR g d and not for TCRa b. By PCR and Southern blot analyses for the Immunoglobulin and TCR (a b
and g d) genes on DNA isolated from the affected lymph node no evidence for a monoclonal population was
found. Fisher et al reported one patient with an accumulation of DN TCR g d T cells in the circulation,
and DN TCR a b T cells in the affected tissue . These two cases demonstrate that ALPS can not only
result in proliferation of TCRa b, but albeit infrequently, also of TCR g d DN T cells. It is important
to distinguish this benign polyclonal proliferation from neoplastic g d + T cell proliferations such as
hepatosplenic g d T cell lymphomas.
Although it is not known what triggers the accumulation of DN T cells in symptomatic
ALPS patients, it may be that the nature of the initial trigger defines the phenotype of the T cells with
respect to a b or g d TCR. Development of lymphadenopathy at a very young age of onset may also
contribute to the accumulation of TCR g d DN T cells.
Usually, patients with ALPS also have an increase of CD5 positive polyclonal B-lymphocytes in the
peripheral blood. The immunophenotype findings are summarized in table 3.
Table 3: Immunophenotype of double negative cells
|CD2, CD3, TCR ab and/or gd|
|CD4 and CD8 |
|Increase HLA class II T-cells|
Decrease CD4/CD25 subset
Increase CD5 positive B cells
Increased IL-10 levels
Cytokine Production by the Double Negative T Cells
Several studies have shown that DN T cells in ALPS patients respond poorly to mitogens or antigens and
fail to produce cytokines on activation. This parallels the results of studies of DN T cells in lpr
mice. An increase in circulating IL-10 levels was detected in ALPS patients as compared to normal
A possible cytotoxic T cell origin is supported by the expression of TIA-1 and perforin in DN T cells,
which are normally associated with CD8+ cytotoxic T cells .
Histology of Lymph Nodes and Spleens Involved By ALPS
The enlarged lymph nodes show marked interfollicular and parafollicular hyperplasia. The expanded
areas are populated by TCRab or gd DN T cells and blasts that are positive for CD3, CD57, CD45RA and
TIA-1, but negative for CD45RO similar to the DN T cells in the peripheral blood. The infiltrate results
from the combination of reduced apoptosis and increased proliferation, as measured by decreased in situ
detection of DNA fragmentation and increased staining with MIB-1, respectively . The proliferation
may be extensive enough to suggest a diagnosis of malignant lymphoma. There is at least one case
overdiagnosed as T cell lymphoma recorded in the literature. ALPS should be considered as a possible
differential diagnosis in adult patients presenting with rare types of T-cell lymphomas . Many of
the lymphocytes and blasts express markers associated with cytotoxicity, such as perforin, TIA-1, and
CD57, whereas CD25 is negative . In addition, most lymph nodes exhibit florid follicular
hyperplasia, often with focal progressive transformation of germinal centers, but in some cases
follicular involution was seen. A polyclonal plasmacytosis is also frequently present. The spleen is
markedly enlarged in virtually all patients, more than 10 time normal size. The marginal zone and the
periarteriolar lymphocyte sheath are prominently involved with spilling over into the red pulp. DN T
cells also can be observed in liver biopsies exhibiting portal triaditis. Taken together, the
histopathological and immunophenotypic findings, particularly in lymph nodes and peripheral blood, are
sufficiently distinctive to suggest a diagnosis of ALPS.
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