| What are type II hypersenstivity reactions? | ➢ Unlike type I reactions, in which antigens interact with
cell-bound IgE immunoglobulins, type II reactions involve
the interaction of circulating immunoglobulins with cellbound antigens.
➢ Antibody-Mediated Type II HS reactions are mediated by IgG or IgM antibodies binding to a cell membraneassociated antigen or a fixed tissues antigen (mistakenly detected as foreign)
➢ The damage caused is thus restricted to the specific cells
(cytolyse) or tissues bearing the antigens.
➢ Reaction times can range from minutes to hours.
➢ Type II HS
Complement Dependent Reactions (CDR)
➢ Type II HS
Antibody-Dependent Cell-mediated Cytotoxicity (ADCC) |
| What is TII HS CDR? | ➢ Antibodies IgG or IgM, generated against cell surface antigens, may be cytotoxic (type IIA) or may have agonistic/antagonistic properties (type IIB) or they are generated against extracellular matrix proteins
➢ The resulting Ag-Ab complexes activate complement (via the classic pathway), leading to cell lysis or extracellular tissue damage.
➢ The target can be a red cell, a virally infected cell, or
a bacterium.
Type IIA /Autoantibodies against blood cells promote
their destruction
➢ IgG or IgM responses to antigens located on the cell
surface lead to the rapid destruction of these cells. |
| What are diseases in CDR TIIHS? | – Transfusion reactions: incompatible RBC's or serum
is transfused.
– Autoimmune hemolytic anemia: antibody is made
against one's own RBC's.
– Erythroblastosis fetalis: maternal IgG crosses the
placenta and attaches to fetal RBC's
Can occur in two ways (complement activsation and intravascular hemolysis or FcR fix on mononuclear phagocytic system) |
| What happens when incompatible RBCs is transfused? | ➢ Among the 19 different human blood group systems, the
group ABO is the most important.
➢ Nearly all individuals make IgM antibodies to the
antigens of the ABO system that they lack
➢ These antibodies do not cross the placenta; they occur
naturally, without prior immunization
➢ If an individual is blood group A, he or she will be
tolerant to A and agglutinate B red cells, and vice versa
for a blood group B individual.
➢ Conversely, a blood group O person will make anti-A and anti-B as natural antibodies and will only tolerate blood
transfusions from group O individuals
➢ When planning a blood transfusion, it is important to
ensure that donor and recipient blood types are
compatible with respect to these major blood groups,
otherwise transfusion reactions will occur |
| What are transfusion reactons? | ➢ Transfusion of allogeneic erythrocytes into an individual
who already has antibodies against them may produce
an immediate reaction; erythrocyte destruction and
symptoms of a 'transfusion reaction'.
➢ Thus, if mismatched blood is transfused, it will cause
blood agglutination, complement activation and
intravascular hemolysis in the recipient
➢ The large pentameric structure of IgM allows for building of bridges between encountered epitopes on molecules that are too distant as to be connected by smaller IgG
➢ The first component of complement C1q consists of six
subunits and reacts with the Fc via its globular heads.
➢ The activation of this component requires the binding of
two globular heads for activation
➢ One molecule of IgM with its pentameric conformation
can easily activate C1q, while the ability of IgG, which has only two sites to activate C1q, is low. |
| What are S&S associated with transfusion reactions? | 1) Inflammatory: Fever/chills, Skin changes (anemia, jaundice), Pain at infusion site
2) Circulatory: Blood pressure changes, Shock, Hemoglobinemia/uria
3) Pulmonary: Dyspnea, orthopnea, wheezing Full respiratory failure
4) Coagulation: Unexplained increase in bleeding DIC
5) Psychological:
a) Sense of unease or impending “doom”!
➢ The symptom include nausea and vomiting, and pain in the back and chest.
➢ These acute transfusion reactions are often seen in
previously unsensitized individuals
➢ Other blood groups, minor blood group systems, induce IgG antibodies, which cause less agglutination than IgM.
➢ Transfusion reactions caused by the minor blood groups are relatively rare, unless repeated transfusions are given |
| How is autoimmune hemolytic anemia? | In males, anemia is typically defined as hemoglobin level
of less than 13.5 gram/100ml, while in women, a hemoglobin level of less than 12.0 gram/100ml is considered to be indicative of anemia.
These definitions may vary slightly depending on the source and the laboratory reference used
Autoimmune hemolytic anemia (AHA) is a group of conditions where a person’s immune system destroys their red blood cells (RBCs) |
| How is approach to autoimmune hemolytic anemia? | Standard blood studies for the workup of suspected
hemolytic anemia include the following:
➢ Complete blood cell count
➢ Serum lactate dehydrogenase (LDH) study
➢ Serum haptoglobin
➢ Indirect bilirubin
➢ Peripheral blood smear (Peripheral smear findings can help in the diagnosis of a concomitant underlying hematologic malignancy associated with hemolysis.)
Other laboratory studies may be directed by history, physical examination, peripheral smear, and other laboratory findings. (DAT, free hb, red blood cell survival, cold agglutinin, G6PD) |
| How is hemolytic anemia workup? | The DAT result is usually positive in autoimmune hemolytic
anemia (AIHA), but it may occasionally be negative in this
disorder.
From 5-10% of all AIHAs are DAT negative.
DAT-negative AIHA has a better prognosis than DAT-positive AIHA.
In addition to hemoglobinuria, either myoglobinuria or
porphyria may result in dark urine.
To rule out these possibilities, the urine should be tested for
free hemoglobin. Hemoglobinuria occurs when the amount of free hemoglobin released during hemolysis exceeds available haptoglobin. Note that haptoglobin is not a reliable way to differentiate between intravascular and
extravascular hemolysis |
| What are types of autoantibodies made in hemolytic anemia? | ➢ Autoimmune hemolytic anemia's can be divided into
three types, depending upon whether they are due to:
oWarm-reactive autoantibodies, which can only react with
antigen at below 370C.
oCold-reactive autoantibodies, which can only react with
antigen at below 370C.
oAntibodies provoked by allergic reactions to drugs
Etiology
Autoimmune hemolytic anemia is caused by abnormalities
extrinsic to the RBC.
It is caused by autoantibodies that react with RBCs at
temperatures ≥ 37° C (warm antibody hemolytic anemia)
or < 37° C (cold agglutinin disease) |
| How are warm auto antibodies? | ➢ Autoantibodies that bind optimally to red blood cells at
37 °C (98.6 °F) are categorized as warm-reacting.
➢ Warm autoantibodies react optimally at temperatures of
35°C–40°C, whereas cold agglutinins and other coldreactive autoantibodies react maximally at 4°C.
➢ Warm antibody hemolytic anemia is the most common
form (80 percent) of autoimmune hemolytic anemia; it
is more common among women
➢ Warm autoantibodies are typically polyclonal IgG
(+/- complement) but may also be IgM or IgA.
➢ Complement activation plays a definitive but limited role
in warm-antibody AIHA (w-AIHA).
➢ Most are IgG1 subclass antibodies reactive with Rh
antigen
IgG3 more activation C, then IgG1 than 2 then 4 |
| How are autoantibodies detected? | ➢ These antibodies are detected by the direct antiglobulin
(Coombs) test => Direct Antiglobulin test (DAT).
➢ The patient’s RBCs are incubated with antibodies to human IgG and C3. If IgG or C3 is bound to RBCs membranes, agglutination occurs - a positive result.
➢ Direct antiglobulin test, demonstrating the presence of
autoantibodies (IgG) alone, (shown here), complement alone, or both IgG + complément (C3) on the surface of the RBCs.
➢ In wAIHA, red cells coated with IgG autoantibodies
(and/or complement), against a cell-surface antigen are
rapidly cleared from the circulation by uptake by Fcγ
receptor-bearing macrophages in the fixed mononuclear phagocytic system.
➢ Additionally, IgG antibodies also have the ability to
weakly activate complement and deposit C3 fragments
on RBCs, which leads to their destruction by Kupffer cells
in the liver |
| When do we suspect AIHA? | ➢ AIHA should be suspected in any patient with a hemolytic anemia (as suggested by the presence of anemia and reticulocytosis).
➢ The peripheral smear usually shows microspherocytes (and the reticulocyte count will be high).
➢ Laboratory tests typically suggest extravascular hemolysis (eg, hemosiderinuria is absent; haptoglobin levels are near normal, schistocytes are absent on smear).
➢ Spherocytosis and a high mean corpuscular hemoglobin
concentration (MCHC) are typical. |
| How can AIHA present? | ➢ AIHA can appear either as a primary disease (50%) or
secondary occurring in association with an underlying
disorder such as;
– Connective tissue diseases (such as SLE, RA, Sjögren’s
syndrome,…),
– Neoplastic diseases (most often lymphomas, LNH, LLC ),
– Hypothyroidism, inflammatory bowel disease, immune
thrombocytopenia,…
– or after use of certain drugs.
– Some patients have several associated diseases at the same time |
| What are S&S of AIHA? | The presenting symptoms of warm antibody AIHA are
commonly related to the anemia itself.
Typically, onset of symptoms is insidious over months.
Less often a patient may note sudden onset of symptoms
of severe anemia and jaundice over a few days.
If the disorder is severe, fever, chest pain, syncope, or
heart failure may occur.
Mild splenomegaly is typical.
In secondary AIHA, the symptoms and signs of the
underlying disease may overshadow the hemolytic
anemia and associated features.
Idiopathic (PE normal) |
| How is tx of AIHA? | ➢ The initial treatment is to diagnose and treat the underlying cause or remove offending agents.
➢ If this is not possible, corticosteroids such as prednisone are often used.
➢ In patients who relapse after corticosteroid cessation or who are refractory to corticosteroids, rituximab is usually used as a second-line drug.
➢ Other treatments include use of additional
immunosuppressive drugs and/or splenectomy. About one
third to one half of patients have a sustained response after
splenectomy. |
| What are S&S of cold reactive autoantibodies? | Cold agglutinin disease manifests as an acute or chronic
hemolytic anemia.
Other cryopathic symptoms or signs may be present (eg,
acrocyanoses, Raynaud syndrome, cold-associated occlusive changes).
Autoantibodies that attach to red blood cells only when
the temperature is below 37 °C are called cold-reacting;
react at 28-31°C and sometimes at 37°C. They belong
primarily to the IgM class
➢ Cooling of blood during passage through acral parts of the circulation allows CA to bind to RBC and cause agglutination. |
| How is mechanism of cold agglutinin disease? | Being a strong complement activator, antigen-bound IgM-CA on the cell surface binds C1 and thereby initiates the classical complement pathway.
➢ C1 esterase activates C4 and C2, generating C3 convertase, which results in the cleavage of C3 to C3a and C3b
➢ Upon returning to central parts of the body with a
temperature of 37°C, IgM-CA detaches from the cell surface, allowing agglutinated erythrocytes to separate from each other, while C3b remains bound.
➢ Activation of complement components C1 through C3 results in covalent binding of C3b to the red cell membrane and renders circulating red cells susceptible to phagocytosis |
| How is effect of temp on CAD? | ➢ Nevertheless, as long as the body temperature remains
at 37 °C, cold-reacting autoantibodies dissociate from the
cell, and hemolysis is not severe.
➢ However, when limbs and skin are exposed to the cold
for long periods of time, the temperature of circulating
blood can be lowered, allowing cold-reacting
autoantibodies to go to work |
| How is tx of cold reactive autoantibodies? | ➢ In many cases, avoidance of cold environments and other triggers of hemolysis may be all that is needed to prevent symptomatic anemia.
➢ In cases associated with a lymphoproliferative disease,
treatment is directed at the underlying disorder.
➢ Rituximab is commonly used, and chemotherapy
regimens used to treat B-cell cancers can be effective
➢ In severe cases, plasmapheresis is an effective temporary
treatment.
➢ Transfusions should be given sparingly, with the blood
warmed through an on-line warmer.
➢ Splenectomy is usually of no value and
immunosuppressants have only modest effectiveness |
| How are ab against platelets and granulocytes? | Mechanisms similar to those that produce autoimmune
hemolytic anemia can result in the formation of
antibodies against platelets and granulocytes, although
autoimmune attacks against these blood cells occur less
frequently. |
| What is immune thrombocytopenia? | ➢ Immune thrombocytopenic purpura (ITP), also known
more recently, as immune thrombocytopenia.
➢ The secondary causes (usually 5-10% of suspected ITP
cases) should be excluded.
➢ Secondary causes could be leukemia, medications (e.g.,
quinine, heparin), lupus erythematosus, and cirrhosis,
HIV, hepatitis C, congenital causes, antiphospholipid
syndrome, von Willebrand factor deficiency and others.
➢ If the exact cause of this condition isn't known, it's called
idiopathic thrombocytopenic purpura |
| How is presentation of IT? | ➢ Typically, it is chronic in adults, but it is usually acute and
self-limited in children.
In adults, most cases of ITP are chronic, manifesting with
an insidious onset, and occur in middle-aged women.
In chronic ITP, for unknown reasons, membrane
glycoproteins (GPs) on the surface of platelets become
immunogenic, stimulating the production of platelet
autoantibodies
➢ In children, most cases of immune thrombocytopenic
purpura (ITP) are acute, manifesting a few weeks after a
viral illness; peripheral smear shows an increased
number of normal or atypical lymphocytes reflecting a
recent viral illness).
In acute ITP, the stimulus for autoantibody production is
unknown; pseudoantigens may be formed by the passive
adsorption of pathogens on platelet surfaces |
| How is mechanism of action in IT? | ➢ In persons with Immune Thrombocytopenia (ITP), platelets are coated with autoantibodies to platelet membrane antigens (usually IgG) with specificity for one or more platelet membrane glycoproteins.
➢ Immune destruction of immunoglobulin-coated platelets is mediated by macrophage, primarily but not exclusively in the spleen.
➢ The spleen is the key organ in the pathophysiology of
ITP, not only because platelet autoantibodies are formed
in the white pulp, but also because mononuclear macrophages in the red pulp destroy immunoglobulincoated platelets
➢ Despite the destruction of platelets by splenic
macrophages, the spleen is normally not enlarged;
Spleen size is normal in the absence of another
underlying condition. |
| How is effect on platelets in IT? | ➢ The resulting shortened life span of platelets in the
circulation, together with incomplete compensation by
increased platelet production by bone marrow
megakaryocytes, results in a decreased platelet count.
➢ Platelet production may also be impaired when antiplatelet antibodies bind to the cells in the bone marrow
that produce platelets, called megakaryocytes |
| How is dx of IT? Tx? | ➢ The diagnosis of ITP is a diagnosis of exclusion.
➢ First, it has to be determined that there are no blood
abnormalities other than a low platelet count, and no
physical signs other than bleeding.
➢ Then, secondary causes (5–10 percent of suspected ITP
cases) should be excluded.
tx: ➢ Corticosteroids remain the drugs of choice for the initial management of acute ITP.
➢ If 6 months of medical management (Corticosteroids, IV immunoglobulin (IVIG)…) fails to increase the platelet count to a safe range (about 30,000/µL), removal of the spleen (the organ in which the main clearance of red cells, platelets, and leukocytes occurs) becomes an option. |
| What is Evans syndrome? | ➢ In approximately 1% of cases, autoimmune hemolytic
anemia and ITP coexist, a condition referred to as Evans
syndrome.
➢ Evans syndrome is the presence of simultaneous or
sequential direct Coombs-positive autoimmune
hemolytic anemia (AIHA) in conjunction with immunemediated thrombocytopenia, with no known underlying etiology
Include: Thrombocytopenia
Anemia
Neutropenia
Pancytopenia |
| How are autoantibodies against neutrophils? | ➢ Autoantibodies against neutrophils, for example, cause
neutropenia, which increases susceptibility to infection
with pyogenic bacteria.
➢ Lysis of nucleated cells by complement is less common
because these cells are better defended by complement
regulatory proteins (nucleated cells require multiple
membrane attack complexes to destroy such cells) |
| How is tissue injury in antibodies provoked by allergies? | ➢ Drugs (or their metabolites) can provoke HS reactions
against blood cells, including erythrocytes and platelets
Drug induce (hemolytic anemia, thrombocytopenia, granulocytopenia) |
| How is drug induced hemolytic anemia? | ➢ Some drugs (eg, alpha-methyldopa, levodopa) stimulate
production of autoantibodies against Rh antigens (in
persons who have been taking the antihypertensive
medication alpha methyldopa for several month).
➢ The antibodies produced are similar to those in patients
with warm-reactive antibody.
➢ However, the condition remits shortly after the cessation
of drug treatment.
➢ The antibody-coated cells are mainly sequestered to the
reticuloendothelial system in the liver and spleen by Fc or
complement-receptor binding.
Others produce antibodies against Abx RBC complex (hapten stable [penicillin/ceph] or unstable [quinidine, sulfo) |
| How are drug induced thrombocytopenias? | The drug (quinine, quinidine…) acts as a hapten, coats platelets or cells, antibodies and complement bind and cells are lysed
The most common cause of type II reactions are
medications including methyldopa, penicillins,
cephalosporins, and hydrochlorothiazide which become
associated with red blood cells or platelets leading to
anemia and thrombocytopenia |
| What is erythroblastosis fetalis? | ➢ Hemolytic Disease of the Newborn (HDNB) occurs when
the mother has been sensitized to antigens on the
infant's erythrocytes and makes IgG antibodies to these
antigens.
➢ Sensitization of the Rh-mother to the Rh+ erythrocytes
usually occurs during birth of the first Rh+ infant, when
some fetal erythrocytes leak back across the placenta
into the material circulation and are recognized by the
material immune system
➢ If she becomes pregnant, and the father is Rh+
the fetus may be Rh+ as well.
➢ If so, the anti-Rh antibodies of the mother can cross the
placenta and cause lysis of the fetal blood cells.
➢ The disease is hemolytic disease of newborns
(erythroblastosis fetalis)
Thus first child is unaffected while others are |
| What are diseases caused by antireceptor Abs Type II HS? | Autoantibodies against cell surface receptors produce
disease by stimulating or blocking receptor function.
Diseases caused by this mechanism include:
– Myasthenia gravis: acetylcholine receptor antibody.
– Graves disease (thyrotoxicosis): anti-TSH receptor
antibody.
– Pernicious anemia: anti-parietal cell antibody
myasthenia gravis, autoantibodies against the
acetylcholine receptors on skeletal muscle cells bind the
receptor and induce its internalization and degradation in
lysosomes, reducing the efficiency of neuromuscular
transmission and causing progressive muscle weakness
Graves' disease is characterized by autoantibodies that act as agonists. TSH receptor antibodies (TRAb) are believed to cause hyperthyroidism of Graves ' disease |
| How is demonstration of grave's disease? | The pathogenicity of anti-TSH R autoantibodies is
demonstrated by the occurrence of neonatal Graves’ disease after passive transplacental transfer of IgG thyroid-stimulating autoantibodies from a mother with Graves’ disease to the fetus
The autoimmune process underlying this disorder is thought
to be provoked by helper T cells that react with thyroid
antigens, although the mechanism is not completely
understood.
➢ Once activated, the self-reactive T cells stimulate B cells to secrete antibodies against several target antigens, including thyroglobulin
➢ Graves’ disease is associated statistically with a group of autoimmune diseases including pernicious anemia,
vitiligo, alopecia, angioedema, myasthenia gravis, and
idiopathic thrombocytopenic purpura.
➢ A weak association is probably present with rheumatoid arthritis and SLE. |
| What is Biermer's disease Pernicious anemia? | ➢ Biermer's disease, also called acquired pernicious
anemia , is a condition in which the body is unable to
properly utilize vitamin B12.
➢ Because vitamin B12 is essential for the formation of red
blood cells , this condition is primarily characterized by
anemia.
➢ Pernicious anemia (PA) is the end state of a progressive
disease known as autoimmune chronic atrophic gastritis.
➢ In this disease, immune-mediated inflammation leads to
destruction of gastric parietal cells with the resultant loss
of intrinsic factor production and the inability to absorb
dietary vitamin B12.
Dx by macrocytic anemia + vit B12 def and anti-parietal cell Abs and intrinsic factor Ab (PCA and IFA) |
| How is good pasture disease example of TIIHS? | Goodpasture's disease, in which antibodies against the
α3-chain of type IV collagen (the collagen in basement
membranes) are deposited in glomerular and lung
basement membrane.
Goodpasture disease is a term used to describe
glomerulonephritis, with or without pulmonary
hemorrhage, and the presence of circulating anti–
glomerular basement membrane (anti-GBM).
➢ Although anti-GBM disease is seen as a prototypic
autoantibody-mediated disease, T cells have a vital role
in disease initiation and progression.
➢ T cells enhance B-cell function and antibody production
and may play a direct pathogenic role in kidney and lung
injury.
Environmental insult + genetics |
| How is pemphigus vulgaris? | ➢ Pemphigus vulgaris is a serious blistering disease that
results from a loss of adhesion between keratinocytes.
➢ Loss of desmosomes results in loss of cohesion
between keratinocytes in the epidermis, and a disruption
of the barrier function served by intact skin
➢ It is an autoimmune disease caused by antibodies directed against desmosomes; )intercellular adhesion structure of epidermal keratinocytes).
➢ Blisters in pemphigus vulgaris are associated with the
binding of IgG autoantibodies to keratinocyte cell surface
molecules
➢ These intercellular or pemphigus vulgaris antibodies bind
to keratinocyte desmosomes and to desmosome-free
areas of the keratinocyte cell membrane
➢ The binding of autoantibodies results in a loss of cell-tocell adhesion, a process termed acantholysis.
➢ The antibody alone is capable of causing blistering
without complement or inflammatory cells |
| How is Bullous pemphigoid? | ➢ Bullous pemphigoid also is a type II HS disorder in which
binding of autoantibodies to basement membrane zone
components creates a cleft between the basal layer of
the epidermis and the basement membrane, resulting in
a subepidermal blister.
➢ Immunofluorescence stains show shows usually C3 and
IgG deposition in the basement membrane zone. |
| How is dermatitis herpeticform? | ➢ Dermatitis herpetiformis is rare autoimmune disease caused by deposition of IgA at the tips of dermal papillae resulting in an inflammatory reaction that tends to form subepidermal blisters.
➢ Some cases of dermatitis herpetiformis are associated with celiac disease, suggesting that the immune response to
gluten-associated antigens in the intestine may contribute to
IgA-mediated disease in the skin |
| How are antibody depedent cell mediated cytotoxicity TIIHS? | ➢ Low concentrations of IgM, IgG or IgE (in the case of
parasites) coat target cells.
Cells exhibiting the foreign antigen are tagged with antibodies (IgG or IgM). These tagged cells are then recognised by natural killer (NK) cells and macrophages (via the Fc region). Neutrophils and eosinophils may also participate in ADCC.
➢ Inflammatory cells such as NK (natural killer) cells,
monocytes/macrophage, and granulocytes with Fc
receptors on its surface are able to recognize and kill a
target cell coated with antibody.
➢ They can lyse, but do not phagocytize the target cells, by elaboration of proteases.
➢ The constant portion of the antibody (Fc region) is bound by Fc receptors on the NK cell, leading to perforin release and NK cell–mediated lysis |
| What are examples of ADCC? | ➢ Examples of ADCC include:
– Transplant rejection
– Immune reactions against parasites
– Immune reactions against neoplasms
➢ ADCC may be involved in the pathophysiology of certain virus-induced immunologic diseases, such as those seen during active response to retroviral infection
➢ While direct complement-mediated lysis takes place
mainly in the circulations and liver, ADCC and
phagocytosis occur preferentially in the spleen and
lymphoid organs. |
