Abstract
The main aims of this study were to determine whether CD4+ and CD8+ cells are present in the normal chambers of the eye in dogs and to verify the hypothesis that uncomplicated cataract may be associated with the local recruitment of CD4+ and CD8+ cells. The presence of CD4+ and CD8+ cells was detected in aqueous humor (AH) of normal and cataract eyes. The study did not reveal differences in the percentage and absolute number of CD4+ cells between normal and cataract eyes. However, the values of these parameters in AH from cataract eyes were approximately 2- and 3-fold higher than in normal eyes, respectively. The mean percentage and absolute count of CD8+ cells increased approximately by 2.7- and 6-fold, respectively, in AH samples from cataract eyes compared to normal ones. The absolute count of CD4+ and CD8+ cells in AH of uveitic eyes was approximately 5- and 3-fold higher than in cataract eyes. The results indicate that CD4+ and CD8+ cells occur constitutively in the normal chambers of the eye in dogs. However, it should be pointed out that both of these cell populations appeared in trace amounts. The development of uncomplicated cataract in dogs may not be immunologically neutral in terms of the local immune response, but it may be associated with the recruitment of CD8+ cells into the eye chambers. This event does not seem to be of an inflammatory nature because it appears on a scale a few times smaller than in the course of uveitis.
Highlights
The eye chambers constitute an immunologically privileged compartment
The development of uncomplicated cataract in dogs may not be immunologically neutral in terms of the local immune response, but it may be associated with the recruitment of CD8+ cells into the eye chambers
It should be emphasized that the absolute number of these cells was extremely low; on average, only 55 ± (SD) 48 and 236 ± 65 events for combined subsets of CD4+ and CD8+ cells were collected for the entire volume of aqueous humor (AH) obtained from normal and cataract eyes, respectively
Summary
The eye chambers constitute an immunologically privileged compartment. The presence of CD4+ and CD8+ cells in the chambers of normal and cataract eyes is a research problem that so far has been explored only fragmentarily. The first aim of our research was to determine whether CD4+ and CD8+ cells are present in the normal chambers of the eye in dogs, and if so, what the relative and absolute counts of these cells are. Blood-aqueous barriers are the fundamental structure restricting the ingress of blood cells into the anterior chamber of the eye Taking into consideration this unique immune privilege status of the eye, we were intrigued whether eye chambers are completely devoid of CD4+ and CD8+ T cells or whether these cells are present at this site. Much is known about tissue-resident memory T (Trm) CD4+ and CD8+ T cells which occupy peripheral tissues and organs without recirculating [3] Another fact that should be taken into consideration is that eye chambers may constitute part of the normal migratory pathway of naïve CD4+ and CD8+ T cells. In the light of these findings, it can be hypothesized that naïve CD4+ and CD8+ T cells may circulate through non-lymphoid tissues, such as the eye, as part of their normal migratory pathway
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