Dengue Literature Review

prM Protein

5 min read

prM Protein

Overview

The pre-membrane (prM) protein is a structural dengue virion protein that is present on immature and partially immature virions. During virion maturation in the trans-Golgi network, furin cleaves prM into the membrane (M) protein and a soluble “pr” fragment that is shed. Fully mature virions retain only M protein on their surface; immature virions retain prM. In practice, furin cleavage is incomplete, and natural dengue infections produce a mixed population of mature (prM-negative) and partially immature (prM-positive) virions. The prM-containing particles are structurally distinct — they are non-infective via the classical receptor-binding entry route — but their presence in the infecting inoculum creates a substrate for a potent, previously underappreciated antibody-mediated enhancement pathway.

Key Points from Literature

Anti-prM as the numerically dominant structural antibody response

Dejnirattisai et al. (2010) isolated 52 human monoclonal antibodies (hmAbs) from B cell lines of 7 DENV-infected Thai donors and characterised each against purified prM and E antigens. Approximately 60% were anti-prM; only ~35% were anti-E (see Dejnirattisai2010 - Anti-prM Antibodies Enhance Dengue ADE, n=3020 B cell lines screened). This was unexpected: the E protein is the major surface protein of mature virions and the traditional focus of dengue immunology, while prM was considered a minor developmental intermediate. The finding implies that the natural dengue infection immunises heavily against prM-bearing particles, producing anti-prM antibodies as the numerically dominant component of the structural humoral response.

Complete cross-reactivity across all four serotypes

All 26 anti-prM hmAbs tested bound DENV-1, -2, -3, and -4 with high avidity by ELISA — fully cross-reactive across serotypes (see Dejnirattisai2010 - Anti-prM Antibodies Enhance Dengue ADE). This contrasts with anti-E hmAbs, which show more serotype-restricted binding profiles consistent with their role in type-specific neutralisation. The cross-reactivity of anti-prM antibodies means that a single primary infection primes a broadly reactive anti-prM population that will bind the prM-bearing particles of any subsequent heterotypic infecting serotype.

Poor neutralisation — a function of incomplete prM cleavage

Anti-prM hmAbs neutralised virus poorly: maximum PRNT plateau of 10–60%, with most unable to achieve >50% neutralisation even at saturating concentrations (see Dejnirattisai2010 - Anti-prM Antibodies Enhance Dengue ADE). The mechanism is the incomplete prM cleavage model: furin cleaves prM on only a fraction of virions released per infectious cycle, leaving a mixture of prM-positive (immature, non-infective via classical receptor binding) and prM-negative (mature, classically infective) particles. Anti-prM antibodies bind the immature fraction but cannot neutralise the mature fraction. In a PRNT where the inoculum is a natural viral stock, the mature fraction proceeds to infect, producing a floor on neutralisation that cannot be overcome regardless of anti-prM antibody concentration.

Potent ADE — up to 10^5-fold enhancement in monocytes and DCs

Anti-prM hmAbs mediated enhancement of infection in primary human monocytes and monocyte-derived dendritic cells at magnitudes up to 10^5-fold over antibody-free controls (see Dejnirattisai2010 - Anti-prM Antibodies Enhance Dengue ADE). Enhancement was FcγR-dependent — blocked by anti-FcγR antibodies. The proposed mechanism: anti-prM-opsonised immature/partially immature particles (which cannot infect via classical receptor binding alone) are taken up by monocytes/DCs via FcγR; once inside, they replicate and release progeny. The magnitude of anti-prM ADE substantially exceeds typical anti-E ADE and may represent the dominant enhancement pathway in secondary dengue infection.

Dengue specificity — contrast with JEV

Anti-JEV serum showed minimal cross-reactivity with DENV prM, indicating that the anti-DENV prM response is dengue-specific rather than a product of broad flavivirus cross-immunity (see Dejnirattisai2010 - Anti-prM Antibodies Enhance Dengue ADE). This matters for interpretation of ADE risk in populations with prior JEV vaccination or infection: JEV immunity does not appear to prime an anti-prM ADE pathway for dengue.

Vaccine implication

CYD-TDV (Dengvaxia), DENVax/TAK-003 (Qdenga), and TV003/TV005 all incorporate native prM sequences alongside E protein. All will therefore prime anti-prM antibody responses with the same cross-reactive, poorly neutralising, ADE-potent profile described above (see Dejnirattisai2010 - Anti-prM Antibodies Enhance Dengue ADE, Dengue Vaccine Candidates). The authors call for heterologous prM design in future vaccine constructs — a challenge that remains open as of the sources in this wiki.

Anti-prM cross-reactivity with HSP60 — molecular mimicry contribution (via Lin2011, confirmed Bhatt2020)

Anti-prM antibodies cross-react with HSP60 on BHK-21 and A549 cell surfaces (established by Lin2011, cited in context of dengue molecular mimicry by Bhatt2020 - Dengue Pathogenesis Review). HSP60 is also a target of anti-NS1 cross-reactivity (see NS1 Protein). The convergence of anti-prM and anti-NS1 antibodies on the same host protein (HSP60) suggests that the auto-cross-reactive burden on HSP60-expressing cells (platelets, endothelial cells) may be driven by two independent antibody populations arising from different viral antigens. This is a potentially additive contribution to NS1 molecular mimicry-mediated pathology that is not yet quantified.

Contradictions & Debates

  • The 10^5-fold enhancement observed in primary monocyte and DC cultures has not been directly validated in an in vivo setting. Whether this magnitude of enhancement translates to higher viraemia in secondary human infections — or whether homeostatic and innate immune constraints attenuate the in vitro effect — is unknown.
  • The mechanism of prM-positive particle infectivity via FcγR is well supported in vitro, but the relative contribution of anti-prM vs. anti-E ADE to total enhanced viral replication in natural secondary infection is unquantified.
  • Why anti-prM antibodies constitute ~60% of the structural humoral response — when E protein is far more abundant on mature virions — remains unexplained. One possibility is that immature or partially immature particles are preferentially presented during natural infection, biasing B cell priming toward prM.

Sources

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