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systemic lupus erythematosus (SLE) 676 systemic lupus erythematosus (SLE)
Lupus erythematosus. Immune deposits at dermal–epidermal junction.
Systemic lupus erythematosus (SLE). Immune deposits at dermal–epidermal
junction.
Diffuse proliferative lupus nephritis.
systemic lupus erythematosus (SLE)
The prototype of connective tissue diseases that involves
multiple systems and an autoimmune etiology. It has an
acute or insidious onset. Patients may experience fever, malaise,
loss of weight, and lethargy. All organ systems may be
involved. Patients form a plethora of autoantibodies, especially
antinuclear autoantibodies. SLE is characterized by
exacerbations and remissions. Patients often have injuries
of the skin, kidneys, joints, and serosal membranes. SLE
occurs in 1 in 2500 people in certain populations and has
a female-to-male predominance of 9:1. Its cause remains
unknown. Antinuclear antibodies produced in SLE fall into
four categories: (1) antibodies against DNA, (2) antibodies
Systemic lupus erythematosus (SLE). Diffuse immune deposits on peripheral
capillary loops.
against histones, (3) antibodies to nonhistone proteins
bound to RNA, and (4) antibodies against nucleolar antigens.
Indirect immunofluorescence is used to detect nuclear
fluorescence patterns that are characteristic for certain
antibodies, such as homogeneous or diffuse staining that
reveals antibodies to histones and deoxyribonucleoprotein;
rim or peripheral staining that signifies antibodies against
double-stranded DNA; speckled patterns that indicate antibodies
to non-DNA nuclear components including histones
and ribonucleoproteins; and the nucleolar pattern, in which
fluorescent spots are observed in the nucleus and reveal
antibodies to nucleolar RNA. Antinuclear antibodies most
closely associated with SLE are anti-double-stranded DNA
and anti-Sm (Smith). The disease appears to have a genetic
predisposition associated with DR2 and DR3 genes of the
major histocompatibility complex (MHC) in Caucasians
of North America. Genes other than human leukocyte
antigen (HLA) genes are also important. In addition to the
anti-double-stranded DNA and anti-Sm antibodies, other
immunologic features of the disease include depressed
serum complement levels, immune deposits in glomerular
basement membranes and at the dermal–epidermal junction,
and the presence of other autoantibodies. Of all the
immunologic abnormalities, the hyperactivity of B cells
is critical to pathogenesis. B cell activation is polyclonal,
leading to the formation of antibodies against self and
nonself antigens. SLE also involves a loss of tolerance to
self constituents, leading to the formation of antinuclear
antibodies. The polyclonal activation leads to antibodies of
essentially all classes in immune deposits found in renal
biopsy specimens by immunofluorescence. In addition
to genetic factors, hormonal and environmental factors
are important in producing B cell activation. Nuclei of
injured cells react with antinuclear antibodies, forming a
homogeneous structure called an LE or hematoxylin body
usually found in neutrophils that have phagocytized the
denatured nuclei of injured cells. Tissue injury is mediated
mostly by an immune complex (type III hypersensitivity).
Autoantibodies specific for erythrocytes, leukocytes, and
platelets also induce injury through a type II hypersensitivity
mechanism. Acute necrotizing vasculitis involves small
arteries and arterioles present in tissues. Fibrinoid necrosis
is classically produced. Most SLE patients exhibit renal