Immune Reconstitution Post Bone Marrow Transplantation
G.M. DAVISON, N. NOVITZKY
Department of Haematology, Groote Schuur Hospital and The Leukaemia Unit. University of Cape Town, South Africa
Abstract
Haematopoietic stem cell transplantation has become a standard form of therapy for many patients with haematological disorders. However,
the outcome of the process, is threatened by infections, graft versus host disease (GVHD) and relapse of the original malignancy. These
are all caused in part by an abnormal immune system. Many factors influence immune recovery post stem cell transplantation.
These include the type of transplant, GVHD, the intense preconditioning process and post transplant
immunosuppression. Similarities between the immune reconstitution post transplantation
and the post natal development have been described. While this may be true for B-cell recovery, many differences have been noted in T-cell reconstitution. By four to eight months post graft infusion in both
allogeneic and autologous transplants B-cell numbers in the peripheral blood have normalised. Functionally however, these cells are abnormal
and both IgG and IgA production can remain below normal levels for many years. To the contrary, T-cell recovery is very different from normal
embryonic development, and CD4+ T-cells take longer to normalise than their CD8+ counterparts. The abnormally low CD4 counts can
persist for more than a year post transplantation and predispose patients to infections. Closer examination of the CD4 population has revealed
that, in the early stages post T-cell depicted transplantation, they are of the memory type (CD45RO +) and that very few naive (CD45RA +)
helper T-cells are produced. In addition, the T-cells are functionally abnormal and are unable to provide the necessary help to B-cells. This
appears to be the result of thymic atrophy caused by age, conditioning for transplantation and
GVHD. Natural killer cells are the first cells to reach normality after transplantation and are able to functionally kill targets within one
month of engraftment. It is thought that natural killer cells defend the body against infection while T and B-cell recovery takes place.
Future research needs to focus on ways of accelerating immune recovery post transplantation. Possible solutions include the use of the
cytokine IL-7 and the re-infusion of graded numbers of donor lymphocytes. Both approaches have given encouraging results.
The Use of the Micronucleus Assay on a Population of Bats Residing in a Monazite Mine
K. MEEHAN, E. TRUTER
Faculty of Applied Sciences, Cape Technikon, South Africa
J.P. SLABBERT
Radiobiology Laboratory, iThemba Labs, Faure
Abstract
Ionising radiation has been well established as a causative agent of carcinogenesis and mutagenesis and results in chromosome breaks
inducing DNA translocations. Biomarkers may be used to determine either the measure or the effect of exposure and may be important
predictors of cancer risk. Although the effects of high doses of short duration have been well documented, the effects of continuous
exposure to low doses of ionising radiation is not as clearly understood. This study evaluated the clastogenic effects of low dose ionising
radiation on a population of bats (Chiroptera) residing in an abandoned monazite mine. Bats were sampled from two areas in the mine, with
external radiation levels averaging 20 µSv/hr (low dose) and 100 µSv/hr (high dose) respectively. A control group of bats was sampled from
a cave with no detectable radiation above normal background levels. The micronucleus assay used to evaluate residual radiation damage
in binucleated lymphocytes showed that the micronucleus frequency was higher in the test group than the control group. This study showed
that the bats exposed to radiation also presented with an increased number of micronuclei in reticulocytes compared to the control group.
The results of the micronucleus assays showed not only a statistically significant difference between test and control groups (p<0,05), but
indicated a dose dependent increase in DNA damage. These assays may be suitable for quantifying subtle increases in DNA damage
resulting from low dose exposure to ionising radiation.
Biological, Social and Environmental Factors Affecting Sexual Transmission of HIV Infection
0.0. OGUNTIBEJU, D. VELDMAN, F. VAN SCHALKWYK
School of Health Technology, Technikon Free State, Bloemfontein. South Africa
Introduction
One of the most complex factors affecting the pathogenesis of human immuno-deficiency virus (HIV) infection is that of sexual transmission.
Sexual transmission of HIV is dependent on a number of factors that are involved in both the person transmitting the virus and the
uninfected partner.
Transmission through sexual contact accounts for about 75% of HIV infection. Sexual transmission of HIV may occur when a sufficient
amount of infectious virus penetrates the mucosa of the genital tract during sexual relation. Factors that increase the amount and virulence
of the virus, weakens the integrity of the localised tissue barriers, interrupt with the production of an effective local and systemic
immunological response may increase the chances of transmission. Several factors are creating a fertile environment for the epidemic:
mass unemployment and economic insecurity beset much of the Sub-Saharan region. The social and cultural norms are increasingly
liberalised and public health services are steadily disintegrating. Reported rates of other sexually transmitted infections are very high.
These compound the odds of HIV being transmitted through unprotected sex. Unprecedented numbers of young people are not
completing their secondary education. With jobs in short supply, many are at the risk of joining a vulnerable group, for example resorting
to sex work.
Host related and environmental factors could possibly amplify the epidemic via the effect on infectivity and rate of partner change. This
article intends to examine the mechanism, socio-economic and biological factors that affect sexual transmission of HIV especially in
the African context.