Gregory R. Moe

Effect of human serum on de-N-acetyl sialic acid epitope expression and antibody activity against N. meningitidis group B.

Antibody-mediated complement-dependent bactericidal activity (BCA) against Neisseria meningitidis (Nm) is correlated with protection against invasive disease. Recently, we showed that murine antibodies elicited by neuraminic acid-containing polysialic acid (NeuPSA) antigens conferred protection against Nm group B (NmB) strains in an infant rat model of meningococcal bacteremia [Moe GR, Bhandari TS, Flitter BA. Vaccines containing de-N-acetyl sialic acid elicit antibodies protective against neisseria meningitidis groups B and C. J Immunol 2009;182(10):6610-7]. However, NeuPSA antibodies did not mediate BCA against NmB strains in vitro despite the presence of NmB-reactive IgG and IgM. Using monoclonal antibodies (mAbs) SEAM 2 and 3, which are reactive with two distinctive NeuPSA epitopes, and an NmB anticapsular mAb, we show that growth in human serum affects expression of NeuPSA epitopes by NmB and is necessary for evaluating anti-NeuPSA functional activity.

Evidence for rosettes as an unrecognized stage in the life cycle of Leishmania parasites.

ABSTRACT. Leishmania parasites, which afflict 12 million people in 88 countries, exist as promastigotes transmitted by insect vectors and as amastigotes residing in mammalian macrophages. Promastigote cells arranged in rosettes have also been described but universally disregarded as a distinct stage in the life cycle. We present evidence that only rosettes of Leishmania major promastigotes express cell surface poly‐α2,8 N‐acetyl neuraminic acid (PSA) and PSA containing de‐N‐acetyl neuraminic acid (NeuPSA). Expression of rosette‐specific PSA antigens was mosaic, with individual promastigotes expressing PSA, NeuPSA or both. A 50 kDa protein was detected by Western blot analysis of a detergent‐insoluble cell fraction with both PSA and NeuPSA‐reactive antibodies. Frequencies of rosette formation as well as cell surface PSA/NeuPSA expression were temperature dependent. Rosettes also engaged in an unusual swarming behavior, congregating into extended clusters. Distinct structures resembling cellular fusion bodies were formed in and released from rosettes. The results indicate that rosettes are an unrecognized stage in the life cycle of Leishmania. We hypothesize that rosettes initiate mating in Leishmania during which PSA/NeuPSA expression plays an important role. Recognizing rosettes as a distinct form of the Leishmania life cycle opens new possibilities for treatment or prevention of disease and, possibly, in vitro genetic recombination without passage of cells through insect vectors.