the epstein  barr virus ( ebv ) was described by michael anthony epstein and yvonne barr , who isolated ebv virus particles from endemic burkitt lymphoma specimens .
ebv is a double stranded dna virus of the herpes virus family and is the most common virus affecting humans .
the infection occurs through oral transmission via saliva . by the age of 40 , over 90  % of the world population has experienced an ebv infection .
ebv also plays a pathogenic role , mainly in the development of several t cell and b cell lymphoproliferations ( see below ) but is also associated with different types of rare epithelial and mesenchymal neoplasms .
ebv is mainly a b - lymphotropic and epitheliotropic virus and rarely infects t cells and nk cells .
the life cycle of ebv is composed of a lytic state and a latency state , the latter allowing lifelong persistence of the virus in the host .
the replication cycle of ebv is composed of three phases : ( i ) entry into either epithelial cells or naive b cells after oropharyngeal transmission , ( ii ) lytic replication , and ( iii ) latency .
once a cell has become infected , the viral capsid dissolves and the dna is transported into the cell nucleus . in epithelial cells ,
the entry of ebv into the cell is usually directly followed by the lytic replication of the virus , which leads to production of infectious virions using the virus s own replication machinery .
ebv persists in b cells throughout the differentiation from naive b cells to germinal center cells to long - lived memory b cells . in memory b cells ,
dependent on the expression of specific ebv - associated proteins and rnas , three different viral latency types have been described , which can be reproduced to a certain extent by immunohistochemical markers   ( table  1).table 1ebv - latency types and expressed antigenslatency typeebv - associated antigens0/ieber , ebna1ii ( default program)eber , ebna1 , lmp1 , lmp2biii ( growth program)eber , ebna1 - 6 , lmp1 , lmp2a  +  blyticall lytic antigens ( e.g. , zebra ) ebv - latency types and expressed antigens
most humans become infected with ebv during childhood , when the infection usually proceeds asymptomatically or with mild symptoms that are undistinguishable from other viral infections .
if the infection occurs in young adults and adolescents , it can manifest as mononucleosis ( glandular fever ) .
ebv tonsillitis differs from unspecific tonsillitis related to other causes in its histologically detectable polymorphic lymphoid infiltration with abundant plasmablasts and occasional hodgkin - like cells expanding in the interfollicular area of the tonsils . in affected lymph nodes , an extension of the interfollicular areas with a similarly polymorphic infiltration to that in tonsils
can be observed . within the peripheral blood and bone marrow , cd8 positive lymphoblasts ( pfeiffer cells )
might be observed . the histomorphological picture of primary ebv infection shares histomorphological features with other ebv - driven lymphoproliferative diseases ( lpd , table  2 ) .
therefore , the definite diagnosis of infectious mononucleosis is based on the following features : ( i ) young patient age , ( ii ) sole or main manifestation in the tonsils , ( iii ) absence of immunosuppression in the patient , and most importantly ( iv ) a serological test indicating ebv primary infection ( positive igm titer).table 2spectrum of polymorphic ebv driven lpd with variable neoplastic potential spectrum of polymorphic ebv driven lpd with variable neoplastic potential following the primary infection , patients become asymptomatic virus carriers with a very limited number of ebv - positive b cells .
a tissue correlate of this phenomenon is the occasional presence of single small ebv - encoded rna ( eber)-positive b cells , so called bystander cells , within lymph nodes , mucosa - associated lymphatic tissue , or lungs .
rare complications of primary ebv infection , such as the chronic active ebv ( caebv ) disease and/or ebv - associated hemophagocytic syndrome have recently been reviewed in this journal .
since the vast majority of humans have been infected by ebv in childhood and adolescence , ebv - associated lpds in adults usually arise from reactivation of the virus from ebv - infected memory cells .
such reactivation is generally considered to consist in an escape from the normal immunosurveillance and preferentially occurs at sites representing the physiological reservoir of ebv - infected b cells , such as the lymphatic tissues and mucosa .
in these patients , age - related decline in immunocompetence is assumed to be the cause of ebv - lpd [ 4 , 5 ] .
however , the diagnostic pathologist should stress that a clinical work - up of the immune status is warranted once an ebv reactivation is detected .
ebv reactivation in adults occurs primarily in the form of ebv - lpd presenting with a polymorphic histological and clinical picture .
dependent on the clinical scenario and the preferential site of involvement , different types of polymorphic ebv - lpd can be distinguished .
they are outlined in table  2 and include polymorphic posttransplantation lymphoproliferations ( ptld ) , ebv - positive mucocutaneous ulceration ( ebvmcu ) , and lymphomatoid granulomatosis . depending on the clinical scenario and the extent of tissue involvement , these conditions cause variable clinical symptoms .
polymorphic ebv - lpd regress in most patients if immunocompetence can be reestablished , e.g. , by withholding immunosuppressive therapy . nevertheless , a subgroup of polymorphic ebv - lpd progress to more aggressive diseases , usually accompanied by a transformation to the morphology of a fully developed lymphoma ( designated as  monomorphic 
polymorphic ebv - associated lymphoproliferations share histomorphological and immunophenotypical features , which are certainly not specific but should alert the histopathologist to an ebv - driven disease when analyzing lymphatic proliferations .
these features include the following : tissue necrosisepithelial ulcerationangiotropic vasculitis - like lymphoid infiltratespolymorphic picture rich in large cells , hodgkin - like cells , plasmablasts and plasma cellsintermingled large t cells ( often cd8 positive)b blasts , with weak cd20 expression and expression of cd30 epithelial ulceration angiotropic vasculitis - like lymphoid infiltrates polymorphic picture rich in large cells , hodgkin - like cells , plasmablasts and plasma cells intermingled large t cells ( often cd8 positive ) b blasts , with weak cd20 expression and expression of cd30 if the clinical scenario ( immunosuppression ) or the histological features are suggestive of an ebv - lpd , testing by eber in situ hybridization should be initiated ( see below ) .
when the diagnosis of an ebv - positive polymorphic lpd has been confirmed by detection of ebv in the tissue , the nomenclature ( classification ) of the disease is dependent on ( i ) the clinical context and ( ii ) the involved site ( table  2 ) .
ebv - lpd histologically resembling a lymphomatoid granulomatosis might occur after organ transplantation , in which case the disorder is named according to both the clinical scenario and the histopathological picture as  ebv - positive polymorphic ptld under the histopathological picture of a lymphomatoid granulomatosis  .
the most important diagnostic message from the pathologist to the treating clinican should be ( i ) the ebv association of the lesion and ( ii ) the clear distinction of polymorphic ebv - lpd from fully developed lymphomas.fig .
a and d illustrates the features of a primary ebv infection in the oral mucosa of a child . as examples of ebv reactivation , an ebv - associated mucocutaneous ulcer in the anal mucosa in a patient treated with azathioprin for myastenia ( b and e ) and a lymphomatoid granulomatosis in the lung of a patient ( c and f ) are shown . as shared features in all lesions necrosis ( arrow ) and angiotropism ( arrow head )
f 400 histomorphology of ebv - associated lymphoproliferative diseases . a and d illustrates the features of a primary ebv infection in the oral mucosa of a child . as examples of ebv reactivation , an ebv - associated mucocutaneous ulcer in the anal mucosa in a patient treated with azathioprin for myastenia ( b and e ) and a lymphomatoid granulomatosis in the lung of a patient ( c and f ) are shown .
as shared features in all lesions necrosis ( arrow ) and angiotropism ( arrow head ) are indicated .
ebv - positive lymphomas occur in immunocompetent patients , but are much more frequent in immunocompromised patients . in the latter patient group ,
the latency type of ebv detectable in the lymphoma cells frequently but not exclusively indicates higher viral activity with expression of more ebv encoded proteins ( latency type 3 ) and sometimes active viral replication .
lymphomas occurring in immunocompetent patients , such as hodgkin lymphoma , usually display latency types 0/1 or 2 with a more restricted pattern of ebv - associated proteins and no viral replication ( table  3 ) .
the diagnostic criteria for these lymphomas have been described elsewhere and do not necessarily require the detection of ebv because of the presence of ebv in the lymphoma cells . in rare cases , detection of ebv is a mandatory diagnostic feature ( e.g. , in ebv - positive lpd of childhood ) .
nevertheless , in certain lymphoma entities , e.g. , nasal and extranasal nk t cell lymphoma , angioimmunoblastic t cell lymphoma , primary effusion lymphoma , and plasmablastic lymphoma , ebv association remains an important clue towards the correct diagnosis .
of further relevance might be the identification of ebv - positive diffuse large b cell lymphoma ( dlbcl ) of the elderly .
histological features that are useful for identifying dlbcl candidates for screening for ebv have been described as angiotropic growth , necrosis , and polymorphic , plasmablastic or hodgkin - like differentiation and expression of cd30 .table 3ebv - positive lymphomas and latency types and their association with immunocompromised statelineageimmunocompetence of patientsentitylatency typeb cellcompetentclassical hodgkin lymphoma2endemic burkitt lymphoma0/1sporadic burkitt lymphoma0/1ebv  +  dlbcl of the elderlyvariableebv  +  dlbcl associated with chronic inflammation ( pyothorax lymphoma)predominantly 3compromisedprimary effusion lymphoma0/1plasmablastic lymphoma0/1lymphomatoid granulomatosis grade 3 and dlbcl arising from the former3monomorphic ptld 
 variablelymphomas associated with hiv infection 
 variablelymphoproliferative disease associated with primary immune disorders 
 variableother iatrogenic immunodeficiency - associated lymphoproliferative disorders 
 3 t cellcompetentangioimmunoblastic t cell lymphoma0/1 or 2extranodal nk / t cell lymphoma2compromisedebv - positive t cell lymphoproliferative disease of childhood and young adults 
 variable 
 diseases under this category are further specified according to histopathology 
 the immunodeficiency in many of these young patients is postulated but not always objectifiable 
 dlbcl diffuse large b cell lymphoma , ptld posttransplant lymphoproliferative disease ebv - positive lymphomas and latency types and their association with immunocompromised state 
 diseases under this category are further specified according to histopathology 
 the immunodeficiency in many of these young patients is postulated but not always objectifiable 
 dlbcl diffuse large b cell lymphoma , ptld posttransplant lymphoproliferative disease
the diagnostic criteria for ebv - positive lymphomas are described in the current who classification . however , distinguishing polymorphic ebv - lpd and a fully developed ebv - positive lymphoma can be challenging .
the most important feature , large sheets of ebv - positive blasts and absence of a polymorphic cellular picture , should raise suspicion of an ebv - positive lymphoma , especially a dlbcl .
a specifically difficult task is the differentiation of a polymorphic ebv - lpd from a fully developed classical hodgkin lymphoma , because the latter may be composed of a similarly polymorphic cellular infiltrate to that of the polymorphic ebv - lpd .
pathologists should be aware of the fact that proteins expressed in hodgkin lymphoma , such as cd15 , can also be observed in polymorphic ebv - lpd , like ebvmcu , and therefore the final diagnosis will depend not only on the histopathological features but also on the clinical context , including the site of involvement .
for example , hodgkin lymphomas rarely involve epithelial barrier organs , but ebvmcu by definition always do ( table  2 ) . in our experience ,
clonality testing is not helpful in differentiating ebv - positive lymphoma from polymorphic lymphoproliferations , as viral - driven lpd can also result in a clonal expansion of t and b cells .
testing for ebna2 expression is useful in some cases , since expression of ebna2 strongly argues against hodgkin lymphoma ( table  2).table 4differential diagnostic of polymorphic ebv - positive lymphoproliferative disease ( lpd ) compared to hodgkin lymphomafeaturehodgkin lymphomapolymorphic ebv  +  lpdhistomorphologymixed cellularity infiltration with hodgkin ( like ) cells , necrosispredominant epitheloid cells and eosinophilspredominant plasmablasts , plasmacells , angiotropismimmunophenotype of large cellscd30  >  cd20cd20  >  cd30expression of ebv antigens eber  +  cells equal to lmp1  +  cells eber  +  large cells only
ebna2 negative eber  +  cells more than lmp1  +  cells eber  +  small and large cells ebna2 + /clinical scenariopredominant immunocompetentpredominant immunocompromisedsite mediastinum nodal >  >  extranodal extranodal >  >  nodal
mucosa differential diagnostic of polymorphic ebv - positive lymphoproliferative disease ( lpd ) compared to hodgkin lymphoma
the question as to which specimen should be tested for ebv depends on the histopathological findings on the one hand and on the clinical context on the other hand .
table  3 summarizes our criteria and favored method of testing for ebv , fig .
if pathologists are confronted with lymphoid tissue histologically resembling inflammatory ( reactive ) tissue in immunocompetent patients , the decision whether or not to test for ebv is primarily based on histological features ( table  3 ) . in immunocompromised patients ,
the method of testing should be eber in situ hybridization , which is most sensitive for detecting ebv , especially in lesions that can not necessarily be expected to express other viral antigens such as lmp1 ( table  3 ) .
since indolent ( low grade ) b cell lymphomas are virtually never associated with ebv , testing can not be recommended . for other entities , which are listed in tables  3 and 5 , testing should be part of the standard diagnostic work - up .
immunohistochemical staining for lmp1 is sufficient for hodgkin lymphoma , since these lymphomas express the latency type 2 .
however , other lymphomas listed in table  5 , such as diffuse large b cell lymphomas , require testing by eber because lmp1 is frequently not detectable.fig .
2an ebv - associated mucocutaneous ulcer in the colonic mucosa ( a hematoxilin and eosin ) .
eber usually labels the majority of ebv - infected cells , whereas lmp1 and ebna2 if positive in the lesion stain only a subset of all ebe - positive cells .
d 400table 5recommendations for selecting tissue specimen and methods for ebv testinglymphomanodal and extranodal lymphatic tissue not presenting overt lymphoma ( polymorphic lpd)histopathological featuresclinical contexttesting by ebertesting by ebertesting by eberb cell lymphomas   endemic burkitt lymhoma hodgkin - like large cells and hodgkin or reed - sternberg cells inherited immunodeficiency   plasmablastic lymphoma   primary effusion lymphoma posttransplantation   pyothorax associated lymphoma   dlbcl with histological features suspicious for ebv association necrosis drug induced immunocompromised state angiotropism of blastic cells   any monomorphic ptld   lymphomatoid granulomatosis plasmablastic infiltrate hiv infectiont cell lymphomas   ailt   extranodal nk / t cell lymphoma   ebv - positive t cell lymphoproliferative disease of childhood and young adultstesting by eber or lmp   hodgkin lymphomatesting by eber , lmp1 and ebna2   differential diagnosis between hodgkin lymphoma and ptld 
 ptld  posttransplantation lymphoproliferative disease , aitl  angioimmunoblastic t cell lymphoma an ebv - associated mucocutaneous ulcer in the colonic mucosa ( a hematoxilin and eosin ) .
eber usually labels the majority of ebv - infected cells , whereas lmp1 and ebna2 if positive in the lesion stain only a subset of all ebe - positive cells .
original magnification a  d 400 recommendations for selecting tissue specimen and methods for ebv testing 
 ptld  posttransplantation lymphoproliferative disease , aitl  angioimmunoblastic t cell lymphoma
although epidemiologic data are lacking , ebv - lpd distinct from overt lymphoma will be increasingly recognized .
this is due on the one hand to the aging of many populations , with an increase in age - associated ebv reactivation . on the other hand , widespread access to commercial assays and
automatization leads to an increasing use of in situ hybridization for eber by diagnostic pathologists .
additionally , newly recognized subgroups of lymphomas , such as the ebv - positive dlbcl of the elderly , require the detection of ebv in more lymphoma entities as part of the diagnostic process .
 lymphoproliferations associated with epstein  barr virus ( ebv ) in adult patients pose a diagnostic challenge for pathologists for several reasons . 
 first , the ebv lymphoproliferations represent a clinically and histologically very broad spectrum ranging from self - limiting lymphoproliferations to manifest malignant lymphomas . 
 second , the classification of these diseases is not solely based on histopathology but rather requires a synopsis of clinical as well as pathological features . and third , a resource - efficient diagnostic procedure demands a deliberate strategy for selecting the tissue specimens that are to be tested for ebv . 
 we describe how the clinical context and histological features may indicate to histopathologists which lymphatic tissues should be tested for the presence of ebv and how these features guide the classification . 
 we provide recommendations as to which biopsy specimens should be investigated for ebv and which methods for detecting viral association are appropriate . 
Introduction
Primary infection by EBVclinical and histological features
Reactivation of EBV in adults
EBV-positive lymphomas
Distinguishing polymorphic EBV-LPD and EBV-positive lymphoma
Recommendations for EBV testing
Perspective