Immunobulous disorder is a auto inflammatory blistering disorder in which flaccid Bullae formation

1. PATHOGENESIS OF IMMUNOBULLOUS
DISORDERS AND UPDATES
-Dr. Apoorva Maheshwari

2. CONTENTS:
1. Introduction
2. Classification
3. Dermo-epidermal junction
4. Pathogenesis of intra-epidermal immunobullous disorders
5. Pathogenesis of sub-epidermal immunobullous disorders
6. Updates in pathogenesis

3. INTRODUCTION:
• Its a group of conditions characterized by antibody mediated autoimmune
responses against structural elements of the skin, resulting in blistering of skin and
mucosae.
• Antibody targets include proteins in the hemidesmosomes and BMZ (pemphigoid
group), desmosomes (pemphigus group) and epidermal type transglutaminase
(dermatitis herpetiformis).
• Immunobullous disorders can be further classified into Intraepidermal
immunobullous diseases and Subepidermal immunobullous diseases.

4. • Intraepidermal immunobullous diseases are characterized by formation of vesicles
within the epidermis. The vesicles are flaccid and rupture easily.
• Subepidermal immunobullous diseases are characterized by formation of vesicles
underneath the epidermis. The vesicles are tense and do not rupture easily.

5. CLASSIFICATION:
INTRA-EPIDERMAL IMMUNOBULLOUS DISORDERS:
These include:
• Pemphigus vulgaris
• Pemphigus foliaceus
• Pemphigus vegetans
• Pemphigus erythematosus
• Pemphigus herpetiformis
• Paraneoplastic pemphigus
• IgA pemphigus

6. SUB-EPIDERMAL IMMUNOBULLOUS DISORDER:
These include:
• Bullous pemphigoid
• Mucous membrane pemphigoid
• Linear IgA disease and Chronic bullous disease of childhood
• Pemphigoid gestationis
• Epidermolysis bullosa acquisita
• Dermatitis herpetiformis
• Bullous systemic lupus erythematous
• And some rare disorders like anti-p200 pemphigoid, lichen planus pemphigoidus
and brunsting perry pemphigoid.

7. DERMO-EPIDERMAL JUNCTION:
Lamina lucida

8. FIRST ZONE:
Tonofilament – Hemidesmosome complex:
• It is the site of attachment of the epithelium to the basement
membrane.
Tonofilaments:
• Also called keratin intermediate filaments, they comprise of keratin
5&14.
• They are fine filamentous structures that maintain the intracellular
architecture & organization of basal cells.
• They course through the basal cells & insert into desmosomes &
hemidesmosomes.

9. Hemidesmosome:
• Numerous electron- dense plaques located in the region of the plasma
membrane of the basal cells along the basement membrane.
Lamina Lucida:
• External to the plasma membrane.
• 25- 50 nm in width.
• Contains the anchoring filaments

10. SECOND ZONE:
Lamina densa:
• Appears as an electron- dense amorphous structure.
• 20-50 nm in width.
• At high magnification, it has a granular fibrous appearance.
• Accounts for 40 -65% of total basement membrane proteins.
• Major proteins component is type IV collagen.
• Heparan sulphate proteoglycans and nidogens are other important
components of lamina densa.

11. THIRD ZONE:
• It contains several microfibrillar structures in which 3 of them can be
distinguished.
Anchoring fibrils:
• They appear as condensed fibrous aggregates 20 - 75 nm in diameter.
• At high resolution, these structures appear to have a cross-striated
banding pattern (stain positive for collagen).

12. • The anchoring fibrils are primarily aggregates of type VII collagen.
• The proximal end inserts into the lamina densa, & the distal end is
integrated into the fibrous network of the dermis.
• Anchoring fibrils may loop back into lamina densa or insert into
anchoring plaques in papillary dermis.

13. • The other 2 types of tubular microfibrils are on the basis of classic
histochemical staining procedures, and have been identified as elastic
– related fibrils.
• The microfibrillar component in the absence of amorphous component
known as Oxytalan fibers.
• The microfibrillar component in the presence of small amounts of
amorphous component known as Elaunin fibers, and in the presence of
abundant amorphous component known as Elastic fibers.

14. • In papillary dermis, oxytalan fibers insert perpendicular to the BMZ,
and merge with elaunin fibers to form a plexus parallel to the axis of
BMZ.
• Thus it can be appreciated that DEJ provides a continuous series of
attachment among the major connecting tissue component of the
reticular dermis & internal cytoskeleton of the basal cells.

16. ELECTRON MICROSCOPIC IMAGE AND SCHEMATIC
DIAGRAM OF DESMOSOME:

18. DESMOSOMAL TARGETS IN SKIN DISEASE:
DESMOSOME COMPONENT: AUTOIMMUNE TARGET:
Desmoglein 1 and 3 Pemphigus foliaceus, pemphigus vulgaris
Desmoglein 2 Pemphigus vulgaris, paraneoplastic pemphigus
Desmoglein 4 Pemphigus vulgaris, pemphigus foliaceus
Desmocollin 1 IgA pemphigus
Desmocollin 3 Pemphigus vulgaris
Desmoplakin I/II, plakophilin and plakoglobin Paraneoplastic pemphigus

19. HEMIDESMOSOME/
BMZ COMPONENT
AUTOIMMUNE TARGET
Hemidesmosomal plaque proteins: • BP230
• Plectin
• Bullous pemphigoid
• Bullous pemphigoid
and cicatricial
pemphigoid
Hemidesmosomal transmembrane
components:
• BP180
• ᾳ6β4 integrin
• Bullous pemphigoid,
cicatricial pemphigoid,
linear IgA disease,
pemphigoid gestationis
• Bullous pemphigoid,
cicatricial pemphigoid
Anchoring filament proteins: • Laminin 332
• Ectodomain of BP180
• Cicatricial pemphigoid
• Linear IgA disease,
Bullous pemphigoid
Anchoring fibril proteins: • Collagen VII • Epidermolysis bullosa
acquisita
HEMIDESMOSOMALAND BMZ TARGETS:

20. INTRA-EPIDERMAL IMMUNOBULLOUS DISEASE:
PEMPHIGUS:
• Pemphigus is a severe chronic autoimmune blistering disease of skin
and mucous membranes.
• Pemhigus is derived from Greek word , ‘pemphix’,meaning blisters.
• Annual incidence of - 0.05 to 2.7 per 100,000.
• Peak incidence – 4th – 6th decade.
• Pemphigus vulgaris (PV) is the most common subtype and comprises
about 80% of patients with pemphigus

21. PATHOGENESIS:
• Central to the pathogenesis of pemphigus is ACANTHOLYSIS
• Acantholysis – is defined as loss of coherence between epidermal cells
due to breakdown of intercellular bridges.
• Caused by autoantibodies directed against desmosomal proteins.
Leading to blister formation.

22. VARIOUS MECHANISM OF ACANTHOLYSIS:
1. Autoantibodies
2. Complement
3. Plasminogen / plasmin system
4. Exogenous factors: Diet
Environmental factors
Drugs
5. Genetic factors

23. AUTOANTIBODIES:
• Autoantibodies are present against various desmosomal proteins in
different types of pemphigus.
• These interfere with functioning of the desmosomes leading to
keratinocyte seperation and blister formation.
• IgG4 is most commonly represented IgG subclass in PV patients.

25. • Mechanism of acantholysis:
a. Steric hindrance
b. Intracellular signalling
c. Conformational change
a. Steric hindrance –
Ag – Ab binding may result in direct steric hindrance and inhibit the
adhesion properties of desmogleins by binding to N-terminal of
desmosomes which are involved in forming inter-cellular junctions.

26. • b. Intracellular signalling

27. • c. conformational change:

28. COMPLEMENT SYSTEM:
• Role of the complement system in blister formation remains a matter of debate.
• Not necessary for induction of acantholysis.
• Could amplify lesions generated by other pathogenic mechanisms.
• Complement enhances acantholysis by:
• Recruitment of inflammatory cells by chemotaxis.
• Release of proteolytic enzymes by these inflammatory cells.

29. PLASMINOGEN/PLASMIN SYSTEM:
• Epidermal keratinocytes synthesize tissue type plasminogen activator
(tPA), urokinase-type plasminogen activator (uPA), a cell surface
receptor for uPA (uPAR, CD 87), as well as some PA-specific
inhibitors (PAIs).

30. EXOGENOUS FACTORS:
• They play an accessory role in pathognesis of pemphigus.
• Infections
• Diet
• Drugs

31. Infections:
• They may lead to induction and/or exacerbation of pemphigus.
• Mechanism :
• Antigen mimicry
• Upregulating and increasing the production of humoral and cellular
factors
• IFN produced by virally responding T cells induces the HLA
expression of class II on keratinocyte cell membranes, making the
structural site of pemphigus antigen immunologically active.

32. • Fogo Selvagem, is an example of antigen mimicry. Autoantibodies of the IgG-4
subclass directed to certain antigens of Simuliidae pruinosum which also react
with epidermal antigens.
• Infectious agents implicated in pathogenesis of pemphigus are:
• Viral:
• Herpes simplex
• EBV
• CMV
• HHV 8
• Bacterial:
• Staphylococcus aureus
• Proteus vulgaris
• Pseudomonas aeruginosa

33. Diet:
• Thiols, isothiocyanates, phenols, and tannins seem to be responsible
for pemphigus induction.
Mechanism:
• These substances may either be incorporated into the Malpighian
epithelia, leading to nonimmunologic biochemical acantholysis.
• May release sequestered antigens from immunologically privileged
sites and also interfere with the immune balance, leading to antibody-
mediated immunologic acantholysis

35. • Drugs:
Drugs that induce pemphigus are divided into three main groups
according to their chemical structure:
• Thiol drugs
• Phenol drugs
• Nonthiol nonphenol drugs including calcium channel blocker, ACE
inhibitors, NSAIDS, pyrazolone derivates, progesterone,
glibenclamide, etc
• Penicillamine was the first drug reported to induce pemphigus

38. • Other exogenous factors implicated are:
• Pesticides
increased risk
• Metal vapours
• Smoking(current or past)- decreased risk (IJD 2002)
• Suggested mechanism:
• Nicotine may interfere with the activity of antibody to the
keratinocyte acetylcholine receptor.
• Immunosuppresive.

39. GENETIC FACTORS:
• Predisposition to pemphigus is linked to genetic factors.
• Certain MHC class II genotypes are common in patients of
pemphigus.

40. CASCADE OF ACANTHOLYSIS:

41. UPDATES IN PATHOGENESIS :
Newer concepts in acantholysis:
• P38 signalling mediated acantholysis:
binding of autoantibodies activates p38 MAPK signalling pathway,
leading to phosphorylation of hsp27 causing actin-keratin reorganisation
thereby causing acantholysis.
• Role of EGFR:
EGFR is a mediator of p38 MAPK pathway and thus inhibition of
EGFR blocks antibody mediated acantholysis in pemphigus

42. • Desmoplakin point mutation enhancing keratinocyte adhesion:
replacement of serine with glycine in mutated desmoplakin(S2849G)
makes it less prone to PKC induced phosphorylation and thus is less
prone to acantholysis.
• Antibodies against AchRᾳ9 and Pemphaxin:
these antibodies have been discovered in about 85% patients with
pemphigus which block Ca++ influx causing desmosome disassembly
and PKC activation.
• Role of regulatory B-cells:
functionally impaired reg B-cells are unable to downregulate IFN-ᾳ
produced by CD4+ cells.

43. Theories on pathogenesis of pemphigus:
• Multiple hit hypothesis:
according to this theory, pemphigus is a complex disease initiated by
atleast three classes of autoantibodies directed against desmosomal,
mitochondrial and other keratinocyte autoantigens.
• Basal cell shrinkage hypothesis and apoptolysis theory:
according to this theory, autoantibody binding leads to cytoskeleton
rupture leading to collapse and shrinkage of keratinocytes, called
apoptolysis.

44. PARANEOPLASTIC PEMPHIGUS:
• Paraneoplastic pemphigus is an autoimmune disorder that is almost
always linked to an underlying lymphoproliferative disorder.
• Characterised by painful, erosive stomatitis, polymorphous cutaneous
lesions that may be blistering, erosive, lichenoid or morbilliform.
• The most common malignancy associated with paraneoplastic
pemphigus is Non-Hodgkin’s lymphoma. Others include chronic
lymphocytic leukemia, castleman’s disease and thymoma.

45. Pathogenesis:
• Tumors can induce autoimmunity by constitutively or anamolously
expressing epithelial proteins.
• These proteins are targeted by antitumor immune response of the body that
cross react with the normal constitutive epithelial proteins of the host.
• The most characteristic and consistently recognized antigens are envoplakin
and periplakin. Others include antibodies against desmoplakin I and
desmoplakin II, bullous pemphigoid Ag1, plectin, and plakoglobin.

46. • Genetic hypothesis: the disease can be a manifestation of more
complex interaction between tumor cells, immune system and specific
genetic background.
• HLA studies performed on two different series of Paraneoplastic
pemphigus patients revealed a significant predominance of HLA class
II DRB*03 and HLA-class I Cw*14 genes.

47. • Dysregulated cytokine production:
Subsets of cases of NHLs, CLL, and Castleman tumors, the tumor
cells secrete massive amounts of IL-6 in vitro.
• IL-6 promotes B-cell differentiation & drives immunoglobulin
production, and dysregulated IL-6 production has been implicated in
pathogenesis of PNP.

48. SUB-EPIDERMAL BULLOUS DISORDER:
BULLOUS PEMPHIGOID:
• It is the most common disorder within the group of sub-epidermal
immunobullous disorders & most frequent autoimmune blistering
disorder in general.
• Incidence: 2.5-66/million/year.
• Mean age : 69 and 83 years with a slight female preponderance.
• Co-morbidities:neurological and psychiatric disorders like cognitive
impairment, Parkinson disease, stroke, epilepsy and multiple sclerosis.

49. PATHOGENESIS:
Autoantibodies:
• In nearly all bullous pemphigoid patients, autoantibodies bind to
BP180{collagen XVII}
• The extracellular portion of the 16th non-collagenous domain (NC16A)
is the immunodominant region & recognized in 75-90% of BP
patients.
• Serum levels of BP180 NC16A-specific IgG antibodies correlate with
the disease activity in these patients.
• IgG4 and IgG1 are the major subclasses of anti-BP180 NC16A
antibodies

50. • IgG reactivity with C-terminal epitopes is associated with mucosal
involvement and more severe disease
• The intracellular domain preferentially targeted at an early clinical
stage.
• The presence of IgE anti‐BP180 NC16A antibodies is associated with
a severe form of BP, longer duration for remission and requirement for
more intensive therapies.
• BP230 (BPAG1) is recognized by 50–70% of BP sera. Also, IgE
antibodies against BP230 were detected in majority of BP sera.

51. Cellular immune response:
• T‐ and B‐cell reactivity against the NH2‐terminal portion of the BP180
ectodomain is associated with severe BP, while the central portion is
more frequently recognized in patients with limited disease.
• Autoreactive T cells in BP patients produced a Th1/Th2 mixed
cytokine profile.
• The number of peripheral follicular helper T cells, a T‐cell subset
known to be pivotal for B‐cell activation, is higher in patients with
active disease compared to healthy volunteers & correlates with serum
levels of anti‐BP180 antibodies.

52. Cytokines and chemokines:
• Elevated levels of IL‐1β, IL‐2, IL‐4, IL‐5, IL‐6, IL‐8, IL‐10, IL‐15,
IL‐16, IL‐17, IL‐21, eotaxin, monocyte chemotactic protein 4
(MCP‐4), TNF‐α and CCL‐18 occur in the sera and/or blister fluids of
BP patients.
• Serum levels of these mediators correlate with the extent of BP skin
lesions pointing to a pathological relevance of these mediators.
• The assumption that Th2‐type cytokines are important in human BP is
supported by the increased frequency of cutaneous
lymphocyte‐associated antigen‐positive IL‐4 and IL‐13 producing
cells in the peripheral blood.

54. Proposed mechanism of blister formation:
1. Anti-BP180 IgG binds to BP180 antigen on the surface of basal
keratinocytes & initiates Fc‐independent events resulting in the
secretion of interleukin (IL)‐6 and IL‐8.
2. The molecular interaction between BP180 antigen and anti-BP180
IgG activates the classical pathway of the complement system (C′).
3. C′ activation products C3a and C5a cause mast cells (MC) to
degranulate.
4. Complement activation and chemokine gradients trigger the
infiltration of inflammatory cells into the upper dermis

55. 5. Their secretion of additional inflammatory mediators further
increases the inflammatory reaction. Finally, granulocytes at the DEJ
release reactive oxygen species and proteases.
6. This ultimately induces dermal–epidermal separation.

56. Proteases:
• The final step of blister formation is mediated by various proteases
including the plasminogen/plasmin system, mast cell proteinase 4,
matrix metalloproteinase 9, α1‐proteinase inhibitor and neutrophil
elastase.
• Plasmin (formed by activation of plasminogen by tPA and uPA) and
mast cell‐specific serine protease 4 activate matrix metalloproteinase 9
which then inactivates α1‐proteinase inhibitor, the physiological
inhibitor of neutrophil elastase.
• The unrestrained activity of neutrophil elastase is then responsible for
the degradation of structural proteins of the DEJ including BP180.

57. Predisposing Factors:
• Several triggers have been implicated in BP onset including trauma,
burns, skin grafting, radiotherapy and UV radiation including sunlight,
UVA1, psoralen and UVA (PUVA), photodynamic therapy & influenza
vaccination.
• BP can be triggered by drugs like frusemide, spironolactone &
phenothiazines.

58. MUCOUS MEMBRANE PEMPHIGOID:
• Defined as an immunobullous disease with autoantibodies against
components of the DEJ and predominant mucosal involvement.
• Previously, the term cicatricial pemphigoid was used synonymously
for MMP. Currently, cicatricial pemphigoid only refers to the rare
clinical variant in which mucous membranes are not predominantly
affected and skin lesions heal with scarring.
• MMP most frequently involves the oral cavity (in 85% paients)
followed by conjunctiva ( 65%), skin (25-30%), nasal cavity (20-
40%), ano-genital area (20%), pharynx (20%), larynx (5-10%) and
oesophagus (5-15%).

59. PATHOGENESIS:
• 6 target antigens have been identified : BP180 (in 75%); BP230 (in
25%); laminin 332 (formerly termed laminin 5 and epiligrin) in 20–
25%; α6 integrin; β4 integrin; and type VII collagen.
• C‐terminal epitopes on BP180 are predominantly recognized in MMP.
• Autoantibodies to α6 integrin have been predominantly detected in
patients with oral lesions and reactivity against β4 integrin in ocular
involvement.

60. • Passive transfer of antilaminin 332 IgG to neonatal or adult mice
lesions could also be induced in mice lacking complement, mast cells
or T cells, suggesting that such antilaminin 332 antibodies elicit
epidermal detachment in an Fc‐independent manner.
• Since scarring is the major pathogenic process in conjunctival disease,
various profibrotic factors were identified, including hsp 47,
connective tissue growth factor, TGF‐β, IL‐4, IL‐5, IL‐13 and TNF‐α

61. LINEAR IgA DISEASE AND CHRONIC BULLOUS DISEASE OF
THE CHILDHOOD:
• Both the diseases are associated with linear IgA deposition at the
dermo-epidermal junction.
• While Linear IgA disease is most frequent autoimmune blistering
disease in infants and childhood, chronic bullous disease of childhood
(CBDC) is a rare occurence.
• CBDC occurs in children less than 5 years. Linear IgA disease has two
peaks – below the age of 5 years and between 60-65 years.
• In both the diseases, there is slight female preponderance.

62. PATHOGENESIS:
• Major target antigen is ectodomain of BP180, more specifically, linear
IgA bullous dermatosis antigen [LABD97] and linear IgA antigen 1
[LAD-1].
• Both these represent C-terminal portions of BP180, the N-termini of
which are located within NC16A domain of BP180.
• The mechanism of blister formation involve IgA and complement-
mediated neutrophil chemotaxis.
• Unlike BP, mast cell degranulation isn’t important.

63. • IgA antibodies are exclusively of IgA1 subclass.
• Majority of LAD sera also contain IgG Ab against BP180. Also, in
most BP sera, IgA anti‐BP180 antibodies can be detected. The two
diseases may thus be regarded as different ends of a continuous
spectrum with some overlap.
• Three immunoreactant patterns have been demonstrated in Linear IgA
disease:
a. IgA deposits in lamina lucida
b. IgA deposits at and below lamina densa
c. IgA deposits above and below lamina densa
• In CBDC, deposits are seen either in lamina lucida or in sublamina
densa.

64. • Schematic diagram of BP180 and its two antigenic fragments

65. PEMPHIGOID GESTATIONIS:
• It is also called as Herpes gestationis .
• It is exclusively associated with pregnancy and typically presents
during late pregnancy with abrupt onset of intensely pruritic urticarial
lesion.
• Flares occur with delivery with approximately 75% of the patients.

66. PATHOGENESIS:
• Pemphigoid gestationis appeared to be caused by an anti basement
membrane zone antibody directed against BP180 , that induces C3
deposition along the dermo-epidermal junction.
• This antibody binds to amniotic basement membrane which is
antigenically similar to skin.
• Women with pemphigoid gestationis show an increased expression of
MHC class II antigens within the villous stroma of the chorionic villi
but not skin.

67. • It has been proposed that the disease is initiated by the aberrant
expression of MHC class II antigen of paternal haplotype within the
placenta which initiates allogenic response to placental BMZ which
cross reacts with skin .
• HLA-DR3 & HLA-DR4 are associated with PG.

68. EPIDERMOLYSIS BULLOSA ACQUISITA:
• It is a clinically heterogenous subepidermal blistering disorder defined
by autoantibodies against type VII collagen.
• Two main clinical sub types can be differentiated:
a) Clasical or mechanobullous form resembling hereditary dystrophic
epidermolysis bullosa
b) An inflammatory variant that mimics bullous pemphigoid, linear IgA
disease or mucous membrane pemphigoid.
• Mean age of onset: 44-54 years.

69. PATHOGENESIS:
• The auto antibodies are directed against homotrimeric type VII
collagen, a constituent of anchoring fibrils.
• Its N terminal 145kDa NC1 domain has been identified as the immune
dominant region.
• Rarely, reactivity against C terminal NC2 or the central collagenous
domain are reported.
• Occassionaly reactivity with other DEJ antigens like BP180, BP230
and laminin 332 have been demonstrated.

70. • Ab binding leads to activation of IL-1 system and the alternative
complement cascade which lead to recruitment of neutrophils at
dermo-epidermal junction. Fc dependent neutrophil recruitment and
activation also takes place.
• Finally there is release of ROS, elastases and MMP9 which induce
dermal-epidermal splitting.
• DIF shows u-serrated pattern which is different from all other
pemphigoid disorders which show n-serrated pattern.

71. DERMATITIS HERPETIFORMIS:
• Dermatitis herpetiformis is a chronic, intensely pruritic skin condition
associated with gluten sensitive enteropathy.
• It is also called Duhring-Brocq disease.
• It typically presents in fourth decade of life with slight male
preponderance.

72. PATHOGENESIS:
• It is characterised by IgA antibodies against epidermal
transglutaminase 3(TG3).
• It has been hypothesised that there is release of TG3 from
keratinocytes into papillary dermis where it binds circulating IgAAb;
or that circulating complexes of TG3 and IgA are deposited in the
skin. Subsequently neutrophilic infiltration ocurrs leading to
subepidermal blistering.
• It has also been hypothesised that IgA antibodies bind initially to TG3
and TG3 crosslinks IgA2 dermal proteins leading to stable long lasting
IgA deposits in the skin.

73. • Increased serum IL-2 receptor and serum IL-8 levels have been seen in
patients of DH creating proinflammatory environment in the skin
necessary for development of skin lessions.
• Genetics: HLA-DQ2 and HLA-DQ8 have been associated with DH.
• Environmental factors: dietary gluten and its constituent gliadin and
iodine exposure can precipitate flares of the disease.

74. BULLOUS SYSTEMIC LUPUS ERYTHEMATOSUS:
• Bullous systemic lupus erythematosus(BSLE) is an auto immune
subepidermal blistering disease that occurs in patients of SLE.
• Blisters and erosions are not restricted to LE lesions , tend to arise in
sun exposed skin and heal without scaring .
• It typically affects women with an African background in the third
decade of life.

75. PATHOGENESIS:
• When antibodies are directed against type VII collagen it is called type
I BSLE. Antibodies against other antigens of DEJ other then type VII
collagen comprise type II BSLE.
• Auto antibodies in type I BSLE predominantly bind to NC1 domain,
in particular the fibronectin like region.

76. SIGNIFICANCE OF KNOWING PATHOGENESIS:
• Knowing pathogenesis helps us in diagnosing cases where the
diagnosis is doubtful.
• Various treatment modalities have come up that target specific
pathogenic mechanism involved. Example: IVIG targets complement
activation, rituximab targets antibody producing B cells.
• Newer under trial medications include erlotinib and lapatinib that
inhibit EGFR pathway activation.