Strategies for Studying Protective Immunity in Humans Outlined
In April of 1991, a group of individuals studying onchocerciasis met
at Woods Hole and discussed strategies to approach vaccine development.
One of the outcomes of this meeting was a strategy to identify groups of
infected and potentially immune individuals. Recently, to follow up on
this strategy, a survey questionnaire was sent to approximately 30 investigators
who have been involved in field and lab studies of human populations living
in areas endemic for onchocerciasis. Twenty three persons responded. The
OAF is grateful to those who sent back their responses to the questionnaire,
and more importantly, who took considerable time to think through a very
tough issue and offer additional comments.
At a meeting of the OAF in February, many house were spent discussing
the issue of immunity to onchocerciasis. The one indomitable fact was that
this subject is more difficult than some might have originally imagined
because of the potential importance of issues such as concomitant immunity
and variations between populations. Nevertheless, drawing on responses
to the questionnaire, the OAF formulated a plan for studies on human populations
with the hope that investigators could be supported to go into the field
to collect similar data sets and serum samples from various regions. Collected
serum samples will be made available as a resource for other investigators
to use in their own laboratories. Although the OAF is suggesting certain
patient categories (see below), investigators are obviously free to approach
patient samples on other levels (for example, as one large population).
In general, it was felt that populations to be studied should reside in
areas with at least a 70-80% prevalence of microfiladermia (as determined
by skin snips on adult males over the age of 20). Skin snips should be
done at 6 body sites, those sites to be determined by the geographic region.
Skin snips should be done at twice (1 year apart) and if possible 3 times
(0, 1 and 2 year). Data and samples from each population should be collected
from 5 specific groups as listed below:
Group 1:
Nonimmune Individuals (Naive exposed/Infected children)
1) aged 5-10 years with heavy exposure
2) children should convert from negative to positive within the last 1
year (or the next time evaluated)
Group 2:
Individuals (over 20 years old) with high mf counts and high nodule
counts
Group 3:
Individuals (over 20 years old) with low mf and low nodule
counts
Group 4:
Individuals (over 20 years old) who are nodule positive (more than
1 nodule) and mf negative with no active onchodermatitis
Note: Groups 2, 3, and 4 represent infected individuals who either lack
any immunity or may be partially or completely immune to one of the parasite
stages.
Group 5: "Immune" Individuals (over 20 years old)
1) negative skin snips and nodules
2) 10 year residence in endemic area
3) exposure equivalent to infected individuals in the population
4) patient history should also be factored in
At this time, several areas are being considered for study. These
include Ecuador (Thomas Nutman and Ronald Guderian, principal investigators),
and Ghana. Other researchers are also being contacted concerning their
possible involvement. With the sample collected from these studies important
antigens may be identified which are differentially recognized by the various
groups. Furthermore, it is hoped that through the study of these individuals
and the sample collections, we will gain further insight into the immune
state in onchocerciasis as well as important epidemiological information.
Persons interested in any aspect of these studies should contact Joe Cook
at the EMCF.
Cahty Steel