The data concerning memory function were divided into three classes using the regression method of finite mixture models (FMMs), and the results of the regression model were then interpreted for all three classes. STATA software (version 16) was used for data analysis, and the error rate for statistical significance was considered as P < 0.05.

Figure 1

Table 1

Class	N	Mean	SD	Percent	Cum.
I	11	63.99	7.01	7	7
II	50	75.01	14.72	33	40
III	89	85.14	6.43	58	100
Total	150	80.25	13.77	100	100

The present study evaluated the memory functions of 150 patients with HIV infection. The descriptive analysis of the data using a density plot showed that the distribution of memory function scores in these patients possessed three separate modes. Therefore, three regression models using FMM were utilized to assess the risk of memory impairment in these patients (Figure 1).

The means ± standard deviations of the memory function scores of HIV+ patients in classes I, II, and III were 63.99 ± 7.02, 75.01 ± 14.72, and 85.14 ± 6.43, respectively, with the lowest score in class I compared to the other two classes. The ratios of patients with memory impairment in the three classes were 7%, 33%, and 58%, respectively (Table 1).

Regarding the risk factors for memory impairment in HIV+ patients, the predictor variables for the regression model were CD4+ T cell count, gender, age, and education level. The results showed that in patients with poorer memory (i.e., those in class I), scores decreased with increasing age (P < 0.001). Also, memory loss was more prominent in women than in men (P < 0.001), and a higher level of education had a positive effect on memory function (P < 0.001). The results also showed that a reduction in CD4+ T cell count increased the risk of memory loss in these patients (P < 0.001). In patients in classes II and III, those who had higher memory function scores than their peers in class I showed no significant relationship between CD4+ T cell count and memory loss (Table 2).

This study was conducted in order to investigate the relationship between the number of CD4+ T cells and memory function in HIV+ patients. The results showed that the patients could be divided into three classes in terms of memory status, where the mean score for memory function was significantly lower in class I patients compared to those in classes II and III. According to the results of the FMM regression model, CD4+ T cells had a protective role against memory loss in HIV+ patients, as indicated by a significantly lower mean number of CD4+ T cells in class I patients than in their counterparts in classes II and III. Previous studies investigating the relationship between memory function and the number of CD4+ T cells have also confirmed this observation, noting that a drop in CD4+ T cell count below 200 could aggravate memory impairment in HIV+ patients8, 16, 17, 18, 19.

In this study, the average CD4+ cell count was 326, slightly below the mean count of 350 reported to be protective against memory loss in an investigation by Nicoletta et al. on 150 patients with HIV20. Progressive decline in CD4+ cell counts is associated with human immunodeficiency virus (HIV) disease progression21. Recent WHO guidelines advise that a CD4+ threshold of ≤ 200 cells/µL should be used to define patients who have advanced HIV disease22.

According to the results of the present study, memory function in HIV+ patients decreased with increasing age. Schouten et al. (2014) showed that HIV-infected individuals were more susceptible to inflammatory diseases that could directly affect multiple organs and indirectly affect cellular metabolic pathways, the circulatory system, and the neuronal system23. Studies using neuroimaging have demonstrated continuing cerebral atrophy in HIV+ patients with disease progression and failure to control the viral load24. The theory that HIV infection accelerates aging is based on a series of results obtained from studies of infected older adults, and the effect is thought to be associated with persistent stimulation of the immune system, chronic low-grade inflammation, and T-cell dysfunction, symptoms that are assumed to be age-related events25. Our findings are consistent with the observation that HIV infection and aging both activate the immune cells residing in the brain, triggering neuroinflammation and neurodegeneration and leading to the loss of cognitive function. Previous studies have also noted an association between increasing age and a decline in verbal memory in HIV+ patients, where the disease stage was reported to be one of the most important predictors of the intensity of verbal memory impairment26. In another study on individuals less than 25 years old, a reduced CD4+ T cell count was associated with a lower level of verbal learning. In addition, increasing age was associated with speech delay and poor cognitive memory27.

In the present study, the level of memory deterioration was more prominent in women compared to men, and a higher educational level had a positive impact on memory retention. Lumbanraja et al. (2018) showed that there was a relationship between red blood cell indices and CD4+ T cell counts in HIV-infected women of childbearing age28. Another study demonstrated that neurological symptoms indicating cognitive disability were more common in HIV+ women than in HIV+ men and that measures of viral load were higher for women than for men29. Despite limited available evidence to date, there are arguments suggesting differences in immune system responses between men and women, and this may explain the phenomena of a greater decrease in the number of CD4+ T cells in HIV+ females and a more pronounced decrease in their cognitive functions.

The results of the present study support the findings of previous studies suggesting a link between CD4+ T cell depletion and memory loss in HIV+ patients. The HIV infection suppresses aspects of the immune system, including CD4+ T helper cells, and leads to memory impairment. Thus, it is necessary for healthcare providers and practitioners to pay attention to memory deterioration and its association with CD4+ T cell count. Patients should be monitored for memory status in parallel with regular checking of their CD4+ T cell counts, and they should receive appropriate supportive and therapeutic measures if necessary. Our findings suggest that future studies should investigate the signaling pathways responsible for the differences in viral load and cognitive disorders between HIV+ men and HIV+ women.

None.

None.

All authors equally contributed to this work, read and approved the final manuscript.

This research was financially supported by the Research and Technology Deputy of Ilam University of Medical Sciences.

Data and materials used and/or analyzed during the current study are available from the corresponding author on reasonable request.

The present study was approved by the research ethics committee of Ilam University of Medical Sciences under the code IR.MEDILAM.REC.1398.116.

Not applicable.

The authors declare that they have no competing interests.