Epstein-Barr virus — Questions

A complete answer covers what the test measures, where it fails, and the rheumatoid-factor pitfall.

What it detects. Heterophile antibodies are immunoglobulin M antibodies produced during Epstein-Barr virus infection that agglutinate red cells of other species (classically sheep or horse). They are not directed against viral antigens themselves, but their appearance is a useful surrogate for acute infection.

Limitations. The test is often negative in young children, can be negative in the first week or two of illness, and gives occasional false positives in lymphoma, liver disease and autoimmune conditions. A negative result therefore does not exclude Epstein-Barr virus, and virus-specific serology is used when the picture is atypical or the heterophile test is unhelpful.

The rheumatoid-factor pitfall. Rheumatoid factor is itself an immunoglobulin M directed against the Fc portion of immunoglobulin G. In immunoglobulin M assays it can bind non-specifically and generate a false-positive immunoglobulin M signal, including a false-positive viral capsid antigen (VCA) immunoglobulin M. Confirming that the immunoglobulin G arm has matured (for instance that Epstein-Barr nuclear antigen (EBNA) immunoglobulin G is present) helps show that an apparent acute result is in fact a past infection.

The intense, itchy maculopapular rash that follows amoxicillin or ampicillin (though not penicillin) during infectious mononucleosis is a non-allergic, immune-mediated phenomenon specific to the illness; it does not mean the patient is allergic to penicillins and does not preclude their later use. It is distinct from the faint, non-itchy rash that around a tenth of patients develop as part of the illness itself.

It is not an immunoglobulin E (IgE)-mediated allergy, a vasculitis or serum sickness, and it is not the viral exanthem.

Antibody to EBNA appears only weeks to months into convalescence and then persists for life, so its absence alongside a positive VCA immunoglobulin M marks a recent, acute primary infection.

Past infection would show VCA immunoglobulin G with EBNA immunoglobulin G positive and VCA immunoglobulin M negative; a susceptible person has no antibodies; reactivation and chronic active disease show EBNA positivity (often with early-antigen antibody), not its absence.

This is classic infectious mononucleosis: fever, exudative pharyngitis, posterior cervical lymphadenopathy, splenomegaly and atypical lymphocytes (reactive T cells, not infected B cells). Epstein-Barr virus is its commonest cause, and a heterophile antibody is usually positive.

Streptococcal pharyngitis gives neither splenomegaly nor atypical lymphocytes; cytomegalovirus causes a heterophile-negative mononucleosis; acute HIV can mimic the picture and should be considered, but is not the usual cause; adenovirus causes pharyngitis without this haematological picture.

On a B cell gp42 binds an HLA (human leukocyte antigen) class II molecule as coreceptor, after gp350/220 has attached to CD21, and the gH/gL heterodimer with gB then drives fusion.

This underlies the tropism switch: epithelial cells, which lack CD21, are entered without gp42 (using integrins and other proteins), so virus made in a B cell carries little gp42 and infects epithelium well, while virus made in epithelium carries gp42 and infects B cells well. CD21 is the attachment receptor, not the gp42 coreceptor.

LMP1 behaves as a constitutively active CD40 receptor, signalling without any ligand and without T-cell help, and so drives the survival and proliferation pathway NF-kB. It is the principal transforming protein of Epstein-Barr virus.

The B-cell-receptor mimic is LMP2A, not LMP1; LMP1 does not directly inhibit p53, amplify c-myc or mimic the interleukin-6 receptor.

LMP2A delivers a tonic signal resembling that of the B-cell receptor, keeping the latently infected B cell alive and blocking the differentiation that would otherwise trigger reactivation, so the cell survives without antigen.

The CD40 mimic is LMP1; the bcl-2 homologue is the separate viral protein BHRF1; the episome is tethered by Epstein-Barr nuclear antigen 1 (EBNA1); a viral DNA polymerase belongs to the lytic cycle.

Epstein-Barr virus is a gammaherpesvirus and the prototype of the genus Lymphocryptovirus; its current species name is Lymphocryptovirus humangamma4.

The other human gammaherpesvirus, Kaposi sarcoma-associated herpesvirus, sits in the genus Rhadinovirus. The alphaherpesviruses (herpes simplex, varicella-zoster) and betaherpesviruses (cytomegalovirus, human herpesviruses 6 and 7) are different subfamilies.

The linear double-stranded DNA genome (about 172 kilobases) circularises on entering the cell into a chromatin-coated episome that the viral protein Epstein-Barr nuclear antigen 1 (EBNA1) tethers to the host chromosomes; the host DNA polymerase then replicates it with the cell. It is not integrated.

Integration, a cytoplasmic linear genome, and an RNA provirus made by reverse transcriptase all describe other viruses; a viral DNA polymerase operates in the lytic cycle, not in latency.

All forms of Burkitt lymphoma share a translocation that places the c-myc oncogene under the control of an immunoglobulin gene, classically t(8;14), which drives constitutive proliferation. It arises as an off-target accident of the antibody-gene machinery during the germinal-centre reaction.

t(14;18) defines follicular lymphoma, t(9;22) chronic myeloid leukaemia, t(11;14) mantle-cell lymphoma; EBNA2 amplification is not the lesion, though EBV contributes in the endemic form.

Epstein-Barr virus growth-transforms resting B lymphocytes, driving them to proliferate indefinitely as lymphoblastoid cell lines; this immortalising capacity is the basis of its oncogenic potential. In the host it is restrained by EBV-specific T cells, which is why transformation manifests as disease where that control fails.

It does not lyse B cells on contact, does not integrate, is not confined to epithelium, and does not need malaria to grow (malaria is a cofactor for endemic Burkitt lymphoma specifically).

The spleen is enlarged in most cases and can rupture, spontaneously or after minor trauma, in roughly 0.1% to 0.5% of patients; though rare it is potentially fatal. The standard precaution is to avoid contact and collision sport for several weeks, until the splenomegaly has resolved.

Lifelong exercise restriction is unnecessary, splenectomy is not preventive, bed rest does not change outcome, and antibiotics have no role.

Epstein-Barr virus attaches to B cells when gp350/220 binds CD21, the complement receptor 2 that normally recognises the C3d fragment of complement; gp42 then engages an HLA (human leukocyte antigen) class II molecule as coreceptor.

The other options are receptors used by unrelated viruses: CD4 by HIV, CD46 by measles, ICAM-1 by major-group rhinoviruses, and CD155 by poliovirus.

The major envelope glycoprotein gp350/220 attaches the virus to the B-cell surface by binding complement receptor 2 (CD21).

gp42 then acts as the coreceptor-binding protein, and gB with the gH/gL heterodimer drives membrane fusion. LMP1 is a latent membrane oncoprotein, not a virion attachment protein.

Nasopharyngeal carcinoma is EBV-positive in essentially every tumour cell regardless of geography, and runs the latency II programme (Epstein-Barr nuclear antigen 1 (EBNA1), LMP1, LMP2 and the EBV-encoded small RNAs (EBERs)). It clusters in southern China and in middle-aged men, and plasma EBV DNA and a rising immunoglobulin A (IgA) antibody to the viral capsid antigen track and even precede the tumour.

Latency 0 expresses no proteins and is the resting reservoir; the heterophile test belongs to acute mononucleosis; the c-myc translocation defines Burkitt lymphoma, not nasopharyngeal carcinoma.

A large prospective cohort found that Epstein-Barr virus infection raised the later risk of multiple sclerosis around thirtyfold, with a marker of nerve injury rising only after EBV seroconversion, and multiple sclerosis is very rare in the EBV-seronegative. EBV is therefore regarded as a necessary cause, though not a sufficient one, since most infected people never develop the disease. The leading mechanism is molecular mimicry, the immune response to Epstein-Barr nuclear antigen 1 (EBNA1) cross-reacting with a central nervous system protein.

The other options reverse or misstate this relationship.

In latency the genome persists as a quiet episome expressing only a restricted set of genes, with no virus produced; this is the state of the lifelong memory B-cell reservoir. The lytic cycle, triggered by the immediate-early proteins BZLF1 and BRLF1, runs the full gene cascade, builds virions, kills the cell and sheds virus into the saliva.

The other options reverse these features.

Aciclovir and its relatives act only on the virus’s lytic replication. By the time mononucleosis presents the viral load has already peaked, and the symptoms are driven by the host T-cell response, not by ongoing viral replication. So antiviral treatment reduces oropharyngeal shedding but shortens neither the illness nor its course.

Epstein-Barr virus is a herpesvirus and is susceptible to aciclovir-class drugs in its lytic phase; the limitation is the immune-mediated nature of the disease, not drug resistance or absorption.

A complete answer links the virus, the malaria cofactor and the genetic lesion, and gives the clinical picture.

The virus. Endemic Burkitt lymphoma is almost universally EBV-positive, the tumour cells showing the most restricted (latency I) programme, with Epstein-Barr nuclear antigen 1 (EBNA1) only.

The malaria cofactor. It maps to the equatorial-African belt of intense Plasmodium falciparum malaria. Chronic malaria drives polyclonal B-cell proliferation, raises the activity of the antibody-gene-editing enzymes, and weakens EBV-specific T-cell control, all of which expand the pool of infected, dividing B cells in which a transforming accident can occur.

The lesion and clinical picture. That accident is the c-myc translocation, classically t(8;14). The result is the commonest childhood cancer of the region, presenting characteristically as a rapidly growing jaw or orbital tumour.