AIDSWEEKLY Plus, 9 Sep 1996
Daniel J. DeNoon, Senior Editor

The vast majority of HIV infections take place across mucosal surfaces. But as Marc Girard of the Pasteur Institute, Paris, has pointed out, very little is known about how these infections occur.

Even less is known about what kinds of immune responses should be evoked to prevent them.

"We know today that more than 90 percent of AIDS cases follow transmission through the mucosa, whether through the genital mucosa or, for mother-to-child transmission, the mucosa of the genital tract and perhaps also of the eye," Girard said. "However, there are a lot of unknowns."

Girard spoke during his introduction to the session "Induced and Natural Mucosal Immunity" at the XI International Conference on AIDS, held July 7-12, 1996, in Vancouver, British Columbia, Canada.

Girard provided a to-do list for future research by noting that the mucosal target cells for HIV are undefined.

"We do not know what are the target cells," he said. "They are supposed to be the Langerhans cells, but we do not know what receptor is supposed to be operative. There is evidence that it may not be the CD4 receptor. There is a possibility that the core receptor is not the one for T-cell- tropic or macrophage tropic cells."

Several research groups have suggested that HIV penetrates the mucosal surface.

"The possibility has been entertained that the virus could be transcytosed by specialized cells such as the M cells, and that then the virus would infect T cells which are under the mucosa," Girard suggested. "But also the same possibility occurs if there are breaches in the mucosa or microlacerations that might explain the role of STDs [sexually transmitted diseases] as a cofactor."

Perhaps more importantly, researchers are still struggling to find out which types of immune responses - if any - can prevent HIV infection across the mucosa.

Girard proposed that the following questions should be answered:

• Is it necessary to elicit secretory IgAs to control HIV at the mucosal level, or can the transudation of IgGs from the plasma be sufficient to provide protection?
• Should IgA or IgA antibodies be neutralizing, or would binding antibodies be sufficient?
• The role(s) of cellular immunity must be better defined. These immune mechanisms include not only cytotoxic lymphocytes (CTLs) but also cells that secrete cytokines and chemokines.
• Can a vaccine that induces local immunity protect against HIV infection? If so, how can such immunity best be induced?

960909
AW960904

Published by Charles Henderson, Publisher. Editorial & Publishing Office: P.O. Box 5528, Atlanta, GA 30307-0528 / Telephone: (800) 633-4931; Subscription Office: P.O. Box 830409, Birmingham, AL 35283-0409 / FAX: (205) 995-1588 http://www.newsrx.net

Copyright © 1996 - Charles Henderson, Publisher. All rights Reserved. Permission to reproduce granted to AEGIS by Charles W. Henderson. Authorization to reproduce for personal use granted granted by C. W. Henderson, Publisher, provided that the fee of US$4.50 per copy, per page is paid directly to the Copyright Clearance Center, 27 Congress Street, Salem, Massachusetts 01970, USA.